Poly-lactic acid synthesis for application in biomedical devices—A review

Poly-lactic acid synthesis for application in biomedical devices—A review
Poly-lactic acid synthesis for application in biomedical devices—A review

Research review paper

Poly-lactic acid synthesis for application in biomedical devices —A review

Astrid https://www.360docs.net/doc/9f6130710.html,sprilla a ,b ,Guillermo A.R.Martinez a ,b ,Betania H.Lunelli a ,AndréL.Jardini a ,b ,Rubens Maciel Filho a ,b ,?

a Laboratory of Optimization,Design and Advanced Control,School of Chemical Engineering,State University of Campinas,Campinas (SP),Brazil b

Institute of Biofabrication,Campinas (SP),Brazil

a b s t r a c t

a r t i c l e i n f o Available online 6July 2011Keywords:Sugarcane Lactic acid Biomaterials

Renewable resources Bioabsorbable polymer

Bioabsorbable polymers are considered a suitable alternative to the improvement and development of numerous applications in medicine.Poly-lactic acid (PLA,)is one of the most promising biopolymers due to the fact that the monomers may produced from non toxic renewable feedstock as well as is naturally occurring organic https://www.360docs.net/doc/9f6130710.html,ctic acid can be made by fermentation of sugars obtained from renewable resources as such sugarcane.Therefore,PLA is an eco-friendly product with better features for use in the human body (nontoxicity).Lactic acid polymers can be synthesized by different processes so as to obtain products with an ample variety of chemical and mechanical properties.Due to their excellent biocompatibility and mechanical properties,PLA and their copolymers are becoming widely used in tissue engineering for function restoration of impaired tissues.In order to maximize the bene ?ts of its use,it is necessary to understand the relationship between PLA material properties,the manufacturing process and the ?nal product with desired characteristics.In this paper,the lactic acid production by fermentation and the polymer synthesis such biomaterial are reviewed.The paper intends to contribute to the critical knowledge and development of suitable use of PLA for biomedical applications.

?2011Elsevier Inc.All rights reserved.

Contents

1.Introduction ..............................................................321

https://www.360docs.net/doc/9f6130710.html,ctic acid ...............................................................322

3.

Poly-lactic acid.............................................................3223.1.Poly-lactic acid properties ....................................................3233.2.Poly-lactid acid synthesis ....................................................3243.3.Kinetics and modeling of PLA ..................................................3254.PLA biomedical applications ......................................................3265.Conclusion ..............................................................327Acknowledgments .............................................................327References .................................................................

327

1.Introduction

The development of biomaterials (biodegradable and bioabsorbable)with the required characteristics to aid in the recovery of tissues damaged by accident or human disease is one of the greatest research challenges involving areas such as medicine and engineering.Bio-polymers offer an alternative to traditional biocompatible materials (metallic and ceramic)and non-biodegradable polymers for a large number of applications (Chen et al.,2002;Nair and Laurencin,2007;Peter et al.,1998;Temenoff and Mikos,2000).Synthetic biodegradable poly-lactones such as poly-lactic acid (PLA),poly-glycolic acid (PGA),and poly-caprolactone (PCL)as well as their copolymers are now commonly used in biomedical devices (Cheng et al.,2009)because of their excellent biocompatibility.These polymers are degraded by simple hydrolysis of the ester bonds,which does not require the presence of enzymes and in turn prevents in ?ammatory reactions.The hydrolytic products from such degradation process are then transformed into non-

Biotechnology Advances 30(2012)321–328

?Corresponding author at:Laboratory of Optimization,Design and Advanced Control,School of Chemical Engineering,State University of Campinas,Campinas (SP),Brazil.Tel.:+551935213958;fax:+551935213965.

E-mail address:maciel@feq.unicamp.br (R.M.

Filho).0734-9750/$–see front matter ?2011Elsevier Inc.All rights reserved.doi:

10.1016/j.biotechadv.2011.06.019

Contents lists available at ScienceDirect

Biotechnology Advances

j ou r n a l h o m e pa g e :ww w.e l s ev i e r.c o m/l o c a t e /b i o t e c h a d v

toxic subproducts that are eliminated through normal cellular activity and urine.

On the other hand,synthetic degradable polyesters have been used in surgery as suture materials and bone?xation devices for about three decades.Back in1973,lactic acid and glycolic acid were proposed as degradable matrices for the sustained delivery of bioactive substances (Auras et al.,2004).Likewise,Poly-lactic acid(PLA)has been demonstrated to be a suitable bioabsorbable polymer for?xation devices such as resorbable plates and screws(Lorenz,2010).Bioabsorb-able?xation devices have been extensively used as dissolvable suture meshes and recently,by orthopedic surgeons(Lovald,2009;Waris et al., 2004).Absorbable systems are highly advantageous when compared with titanium plates or other metallic implants given that they do not erode bone when placed in the human body(Dearnaley et al.,2007; Lindqvist et al.,1992).In addition,bioabsorbable devices do not require a second surgery to remove the implant–which reduces medical costs–and allow for the gradual recovery of tissue function as the device is degraded.Moreover,synthetic bioabsorbable polymers can stimulate isolated cells to regenerate tissues and release drugs such as painkillers, anti-in?ammatories and antibiotics,which has recently motivated their study as scaffolds for cell transplantation,both in vitro and in vivo(Chen et al.,2006;Dai,et al.,2010;Kulkarni et al.,2010).Another desirable feature of resorbable plates is that,once resorbed,they do not block computed tomography(CT)scans,which facilitates subsequent medical imaging evaluations.

Regarding PLA,it has an extensive mechanical property pro?le and it is thermoplastic with high biocompatibility and biodegradability properties(Auras et al.,2004;Gupta et al.,2007).PLA is obtained from lactic acid and converted back to the latter one when hydrolytically https://www.360docs.net/doc/9f6130710.html,ctic acid is a naturally occurring organic acid that can be produced by fermentation of sugars obtained from renewable resources such as sugarcane.Therefore,PLA can be produced and used in an environmentally friendly cycle.

Although there are multiple ways to fabricate PLA,none of them is simple or easy to execute.PLA synthesis requires rigorous control of conditions(temperature,pressure and pH),the use of catalysts and long polymerization times,which implies high energy consumption.In order to understand reaction behavior,kinetic studies of PLA synthesis have been conducted by means of modern simulators,which offer a powerful tool to determine the optimal conditions for obtaining the desired PLA polymer for a speci?c application.This review summarizes information about the properties and applications of poly-lactic acid as well as the different synthesis methods that are currently employed for its https://www.360docs.net/doc/9f6130710.html,ctic acid production process from renewable resources is also reviewed.

https://www.360docs.net/doc/9f6130710.html,ctic acid

Lactic acid(2-hydroxypropionic acid)is a simple chiral molecule that exists as two enantiomers,L-and D-lactic acid(Fig.1),which differ in their effect on polarized light.The optically inactive D,L or meso form is an equimolar(racemic)mixture of D(?)and L(+)isomers(Gupta et al.,2007).It is considered the most potential monomer for chemical conversions because it contains a carboxylic and a hydroxyl group (Varadarajan and Miller,1999).

Lactic acid production has a great worldwide demand due to its versatile applications in food,pharmaceutical,textile,leather,and chemical industries(John et al.,2009)and as monomer in the production of biodegradable polymers(PLA)(Adsul et al.,2007).Lactic acid can in?uence the metabolic function of cells in a variety of ways,as it can serve as an energy substrate and given its uncharged character and small size,it can permeate through the lipid membrane.Also,lactate is capable of entering cells via the monocarboxylate transporter(MCT) protein shuttle system(Philp et al.,2005).Once inside the cell,lactate is converted to glucose,serving as an energy source in the Cori cycle.In addition to its role as an energy substrate for cells,lactic acid has been shown to have antioxidant properties that may serve to protect cells from damage due to free radicals that are naturally produced throughout the cell life cycle(Lampe et al.,2009).

Lactic acid can be produced by fermentative or chemical synthesis. The chemical synthesis is mainly based on the hydrolysis of lactonitrile by a strong acid,where a racemic mixture of the two forms(D(?)and L(+))lactic acid is produced.The biotechnological production of lactic acid has received signi?cant interest,since it is an attractive process in terms of its environmental impact and its combination of low production cost from sugarcane fermentation, decreased fossil-based feedstock dependency,reduced CO2emission, biocatalyst use,and high product speci?city(Lunelli et al.,2010)and, additionally,production of optically pure L-or D-lactic acid,depending on the strain selected(Adsul et al.,2007).

Approximately90%of the total lactic acid produced worldwide is made by bacterial fermentation and the remaining portion is produced synthetically by the hydrolysis of lactonitrile.The petrochemical scheme of monomer production was prevalent until1990,when a more economic fermentation approach was developed(Adsul et al.,2007; Gupta et al.,2007).

The fermentation processes to obtain lactic acid can be classi?ed according to the type of bacteria used.In the heterofermentative process,equimolar amounts of lactic acid,acetic acid,ethanol,and carbon dioxide are formed from hexose,whereas in the homofermen-tative process only lactic acid is produced from hexose metabolism (Auras et al.,2004;Garvie,1980;Hofvendahl and Hahn-H?gerdal,2000; Thomas et al.,1979).Fig.2shows the catabolic pathways for lactic acid production using lactic acid bacteria.

On the other hand,the carbon source for microbial production of lactic acid can be either sugar in pure form such as glucose,sucrose, lactose or sugar containing materials such as molasses,whey,sugarcane bagasse,cassava bagasse,and starchy materials from potato,tapioca, wheat and barley.Sucrose-containing materials such as molasses are commonly exploited raw materials for lactic acid production because they represent cheaper alternatives(John et al.,2007;Lunelli et al., 2010).Sugarcane bagasse is reported to be used as support for lactic acid production by Rhizopus oryzae and Lactobacillus in solid-state fermen-tation(SSF)by supplementing sugars or starch hydrolysates as carbon source(Rojan et al.2005).Brazil is the world's largest sugarcane producer with648,921.280million tons per year in2008,which generated about130million tons of bagasse on dry weight basis, according to FAO Statistics Division(2010),what may be an extra incentive to have a competitive lactic acid industry.

3.Poly-lactic acid

PLA is a highly versatile biodegradable polymer,which can be tailor-made into different resin grades for processing into a wide spectrum of products.Because lactic acid is a chiral molecule existing in L and D isomers,the term“poly-lactic acid”refers to a family of polymers:pure poly-L-lactic acid(PLLA),pure poly-D-lactic acid (PDLA),and poly-D,L-lactic acid(PDLLA)(Grif?th,2000).The L-isomer is a biological metabolite and constitutes the main fraction of

PLA Fig.1.L-and D-lactic acid.

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derived from renewable sources since the majority of lactic acid from biological sources exists in this form.Depending on the composition of the optically active L -and D ,L -enantiomers,PLA can crystallize in three forms (α,β,and γ)(Lim et al.,2008).

PLA was discovered in 1932by Carothers (DuPont)who produced a low molecular weight product by heating lactic acid under vacuum.In 1954Du Pont produced and patented a polymer with higher molecular weight.In 1968Santis and Kovacs reported on the pseudo orthorhombic crystal structure of PLLA,which was a left-handed helix conformation of the α-form (S?dergard and Stolt,2002).Lactic acid based polymers ?rst became commercially successful as ?ber materials for resorbable sutures.After this,a number of different prosthetic devices have been developed (Auras et al.,2004).Nowadays,PLA resins are approved by the US Food and Drug Administration (FDA)and European regulatory authorities for all food applications and some chirurgical applications such as drug releasing systems (Lampe et al.,2009).

Likewise,PLLA has gained great attention because of its excellent biocompatibility and mechanical properties.However,its long degra-dation times coupled with the high crystallinity of its fragments can cause in ?ammatory reactions in the body.In order to overcome this,PLLA can be used as a material combination of L -lactic and D ,L -lactic acid monomers,being the latter rapidly degraded without formation of crystalline fragments during this process (Fukushima and Kimura,2008).

The chemistry of PLA involves the processing and polymerization of lactic acid monomer.PLA is a chiral polymer containing asymmetric carbon atoms with a helical conformation.It has stereocenters in its repeating unit,which can exhibit two structures of maximum order,that is,isotactic and syndiotactic.Isotactic polymers contain sequen-tial stereocenters of the same relative con ?guration,while syndio-tactic polymers contain sequential stereocenters of opposite relative con ?guration (Auras et al.,2010).Isotactic and optically active PLLA and PDLA are crystalline,whereas relatively atactic and optically inactive PDLLA is amorphous (Bouapao et al.,2009).Monomer dyads in the PLA chain may contain identical stereocenters (L :L or D :D )or enantiomeric stereocenters (L /D ).

3.1.Poly-lactic acid properties

PLAs properties have been the subject of extensive research (Malmgren et al.,2006).The stereochemistry and thermal history have direct in ?uence on PLA crystallinity,and therefore,on its properties in general.PLA with PLLA content higher than 90%tends to be crystalline,while the lower optically pure is amorphous.The melting temperature (Tm),and the glass transition temperature (Tg)of PLA decrease with decreasing amounts of PLLA (Auras et al.,2010).Physical characteristics such as density,heat capacity,and

mechanical

Fig.2.Metabolic pathways for lactic acid production.(A)Embden –Meyerhof –Parnas;(B)6-phosphogluconate/phosphoketolase (adapted from Axelsson,2004).

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and rheological properties of PLA are dependent on its transition temperatures (Henton et al.,2005).

For amorphous PLA,the glass transition temperature (Tg)is one the most important parameters since dramatic changes in polymer chain mobility take place at and above Tg.For semicrystalline PLA,both Tg and melting temperature (Tm)are important physical parameter for predicting PLA behavior (Auras et al.,2004;Bouapao et al.,2009;Yamane and Sasai,2003).The melt enthalpy estimated for an enantiopure PLA of 100%crystallinity (ΔH°m )is 93J/g;it is the value most often referred to in the literature although higher values (up to 148J/g)also have been reported (S?dergard and Stolt,2002).

The density of amorphous and crystalline PLLA has been reported as 1.248g ml ?1and 1.290g ml ?1,respectively.The density of solid polylactide was reported as 1.36g cm ?3for l-lactide,1.33g cm ?3for meso-lactide,1.36g cm ?3for crystalline polylactide and 1.25g cm ?3for amorphous polylactide (Auras et al.,2004).In general,PLA products are soluble in dioxane,acetonitrile,chloroform,methylene chloride,1,1,2-trichloroethane and dichloroacetic acid.Ethyl benzene,toluene,acetone and tetrahydrofuran only partly dissolve polylactides when cold,though they are readily soluble in these solvents when heated to boiling https://www.360docs.net/doc/9f6130710.html,ctid acid based polymers are not soluble in water,alcohols as methanol,ethanol and propylene glycol and unsubtituted hydrocarbons (e.g.hexane and heptane).Crystalline PLLA is not soluble in acetone,ethyl acetate or tetrahydrofuran (Nampoothiri et al.,2010).Some of PLAs properties are cited in Table 1.

Few stereocomplex such as PLA can be produced by enantiomers with the identical chemical composition but with different steric structure.Since discovery in 1987,the stereocomplex between poly (L -lactide)(PLLA)and poly(D -lactide)(PDLA)have been intensively studied by preparations,structural,functional properties and applica-bility (Quynh et al.,2008).The PLA properties may be controlled through the use of special catalysts isotactic and syndiotactic content with different enantiometric units (Gupta et al.,2007).

PLA also can be tailored by formulation involving co-polymerizing of the lactide with other lactones-type monomers,a hydrophilic macro-monomers (polyethylene glycol (PEG)),or other monomers with functional groups (such as amino and carboxylic groups,etc.),and blending PLA with other materials (Cheng et al.,2009).Blending can radically alter the resultant properties,which depend sensitively on the mechanical properties of the components as well as the blend microstructure and the interface between the phases (Broz et al.,2003).Broz et al.(2003)prepared a series of blends of the biodegradable polymers poly(D ,L -lactic acid)and poly(ε-caprolactone)by varying mass fraction across the range of compositions.Polymers made from ε-caprolactone are excellent drug permeation products.However,mechanical and physical properties need to be enhanced by copoly-merization or blending (Auras et al.,2004;Wang et al.,1999).

PLA degrades primarily by hydrolysis,after several months exposure to moisture.Polylactide degradation occurs in two stages.First,random non-enzymatic chain scission of the ester groups leads to a reduction in molecular weight.In the second stage,the molecular

weight is reduced until the lactic acid and low molecular weight oligomers are naturally metabolized by microorganisms to yield carbon dioxide and water (Oyama et al.2009:Auras et al.,2004).

The polymer degradation rate is mainly determined by polymer reactivity with water and catalysts.Any factor which affects the reactivity and the accessibility,such as particle size and shape,temperature,moisture,crystallinity,%isomer,residual lactic acid concentration,molecular weight,water diffusion and metal impurities from the catalyst,will affect the polymer degradation rate (Auras et al.,2004;Bleach et al.,2001;Cha and Pitt,1990;Drumright et al.,2000;Tsuji and Ishida,2003).The in vivo and in vitro degradation have been evaluated for polylactide surgical implants.In vitro studies showed that the pH of the solution does play a role in the in vitro degradation,and that,an in vivo study can be used as a predictor of the in vivo degradation of PLA (Auras et al.,2004;Mainil-Varlet,1997).

3.2.Poly-lactid acid synthesis

Polymers based on lactic acid (PLA)are a most promising category of polymers made from renewable resources (Auras et al.,2010).PLA can be prepared by different polymerization process from lactic acid including:polycondensation,ring opening polymerization and by direct methods like azeotopic dehydration and enzymatic polymerization (Garlotta,2001).Currently,direct polymerization and ring opening polymerization are the most used production techniques.Fig.3shows the main methods for PLA synthesis.

Condensation polymerization (polycondensation)includes solution polycondensation and melts polycondensation,and is the least expensive route.However,it is very dif ?cult to obtain a solvent-free high molecular weight poly-lactic acid for these routes (Auras et al.,2004).In direct polycondensation,solvents and/or catalysts are used under high vacuum and temperatures for the removal of water produced in the condensation.The resultant polymer is a low to intermediate molecular weight material,which can be used as is,or coupled with isocyanates,epoxides or peroxide to produce a range of molecular weights (Gupta et al.,2007).Achmad et al.(2009),report the synthesis of PLA by direct polymeriza-tion without catalysts,solvents and initiators by varying the temperature from 150to 250°C and the pressure from atmosphere pressure to vacuum for 96h.The Mitsui Toatsu Chemical Company polymerized poly-DL -lactic acid (PDLLA)using direct solution polycondensation,in which lactic acid,catalysts,and organic solvent with high boiling point were mixed in a reactor.The resultant product shows a molecular weight (MW)of about 300,000(Cheng et al.,2009).

Polycondensation method produces oligomers with average molecular weights several tens of thousands and other side reactions also can occur,such transesteri ?cation,resulting in the formation of ring structures as lactide.These side reactions have a negative in ?uence on properties of the ?nal polymer (Auras et al.,2010).That subproducts production cannot be excluded,but can be controlled by the use of different catalysts and functionalization agents,as well as by varying the polymerization conditions (Mehta et al.,2005).

Lactid acid direct condensation is carry out in three stages:removal of the free water,oligomer polycondensation and melt condensation of high molecular weight PLA.In ?rst and third stages,the removal of water is the rate-determining step.For the second one,the rate-determining step is the chemical reaction,which depends on the catalyst used (Auras et al.,2010).The direct polycondensation of lactic acid in bulk is not applied on a large scale,because of the competitive reaction of lactide formation and the simultaneously occurring degradation process (Dutkiewicz et al.,2003).

In the sequential melt/solid-state polycondensation,besides the three mentioned steps (i.e.,removal of the free water content,oligomer polycondensation,and melt polycondensation)is utilized an additional fourth stage.In the fourth stage,the melt-polycondensated PLA is cooled below its melting temperature,followed by particle formation,which

Table 1

Lactid acid polymers properties (adapted from Nampoothiri et al.,2010and S?dergard and Stolt,2002).

Lactic acid polymers Glass transition temperature

Tg (°C)Melting

temperature Tm (°C)Density (g/cm 3)Good solubility in solvents PLLA 55–80173–178 1.290Chloroform,furan,dioxane and dioxolane.

PDLLA

43–53120–170 1.25PLLA solvents and acetone,ethyl lactate,

tetrahydrofuran,ethyl

acetate,dimethylsulfoxide,N,N xylene and

dimethylformamide.

PDLA

40–50

120–150

1.248

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then subjected to a crystallization process (Auras et al.,2010;Fukushima and Kimura,2008).

Chain extension is effective way to achieve high molecular weight lactic acid-based polymers by polycondensation (Gu et al.,2008).In this method the intermediate low molecular weight is to treat polymers with chain extenders which link the low molecular weight prepolymer into a polymer of high molecular weight.Gu et al.,2008,obtained polymer with a molecular weight (Mv)of 27500g mol ?1after 40min of chain extension at 180°C using 1,6-hexamethylene diisocyanate as the chain extender.

Ring-opening polymerization (ROP)is the most commonly route to achieve high molecular weight (Auras et al.,2010).This process occurs by ring opening of the lactic acid cyclic dimmer (lactide)in the presence of catalyst.The process consists of three steps:polycondensation,depolymerization and ring opening polymerization (see Fig.3).This route requires additional steps of puri ?cation which is relatively complicated and expensive.Catalytic ring-opening polymerization of the lactide intermediate results in PLA with controlled molecular weight (Kim et al.,2009).By controlling residence time and temperatures in combination with catalyst type and concentration,it is possible to control the ratio and sequence of D -and L -lactic acid units in the ?nal polymer (Gupta et al.,2007).

On the other hand,ring-opening polymerization of lactide can be carried out in melt,bulk,or in solution and by cationic,anionic,and coordination-insertion mechanisms depending on the catalyst.Various types of initiators have been successfully tested,but among them,stannous octoate is usually preferred because it provides high reaction rate,high conversion rate,and high molecular weights,even under rather mild polymerization conditions (Mehta et al.,2005).

Azeotropic dehydration is a direct method for synthesis of high molecular weight PLA (Garlotta,2001).In this route,the removal of water formed from the reaction medium becomes relatively easier and a higher molecular weight of the PLA is achievable (Auras et al.,2010).Kim and Woo (2002)obtained PLA of Mv about 33000through the azeotropic dehydration at 138°C for 48?72h using a molecular sieve as a drying agent and m-xylene as a solvent.

Enzymatic polymerization emerges as one of the most viable alternatives and is an environmentally benign method that can be carried out under mild conditions.This methodology can provide adequate control of the polymerization process (Cheng et al.,2009),but

the literature about enzymatic polymerization is poor.Chanfreau et al.(2010),reported the enzymatic synthesis of poly-L -lactide using a liquid ionic (1-hexyl-3-ethylimidazolium hexa ?uorophosphate [HMIM][PF6])mediated by the enzyme lipase B from Candida antarctica (Novozyme 435).The highest PLLA yield (63%)was attained at 90°C with a molecular weight (Mn)of 37.89103g/mol (Chanfreau et al.,2010).3.3.Kinetics and modeling of PLA

In contrast with the extensive experimental work about polymeriza-tion reactions,only few publications deal with the mathematical modeling of such reactions or at least on the evaluation of the corresponding rate coef ?cients (Yu et al.,2009).PLA production can be carried out from both lactic acid and its dimer cyclic (lactide)as the monomer.

The use of lactide as monomer or intermediate product leads to a “Ring Opening Polymerization ”(ROP),which refers to the opening of dimer rings in order to form polymer chains.Several authors have worked in the modeling of catalyzed lactide ROP (Puaux et al.,2007;Yu et al.,2009).According to Yu et al.(2009),the ?rst systematic kinetic analysis of PLA ROP catalyzed by Sn(Oct)2was reported by Eenink (1987),although impurities were not accounted for in such kinetic https://www.360docs.net/doc/9f6130710.html,ter on,Zhang et al.(1994),found that hydroxyl and carboxylic acids strongly affect reaction rates.On the other hand,reversible reactions were included in the lactide polymerization model proposed by Witzke et al.(1997).More recently,researchers have developed models based on the cationic mechanism,which involves irreversible initiation and propagation steps as well as irreversible chain transfer to monomer and impurities (Mehta,2007;Puaux et al.,2007).

The following reactions (R1–R3)represent the polymerization models for PLA synthesis by ring opening proposed by Mehta (2007).This type of reaction is also considered a chain-growth polymerization,and therefore,it is divided into three mains steps:initiation,propagation and termination,having each one of them a different rate constant.M +I →k 0

P 1eR1T

P j +M →k j

P j

+1;

j =1;2;3;…

eR2TP j +M →k t

M j +P 1

eR3

T

Fig.3.Synthesis methods for Poly(Lactic Acid)(adapted from Garlotta,2001and Auras et al.,2010).

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where k 0is the initiation rate constant,M is the monomer,I is the initiator and P 1is the activated polymer of one unit.P j is the active polymer chain of j units and the rate constant of propagation reaction is k j ,which refers to the jth propagation step on a chain.M j is the deactivated polymer of j repeat units that will not react any further,and k t is the termination rate constant.Regarding the termination step,Mehta (2007),proposed two alternative ways,being water-like impurities considered in the ?rst method and intermolecular chain transfers accounted for in the second one.The mass balance equations for a batch reactor were written for the above kinetic scheme as follows:d M ?

dt =?M ? k 0I ? +∑n j =1k j P j h i +∑n

j =1k tj P j h i ()

eEq :1T

d I ?

dt

=?k 0I ? M ? eEq :2T

d P 1?

=k 0I ? M ? ?k 1P 1? M ? +∑n j =2k tj P j h i M ? eEq :3T

d P j h i dt

=M ? k j à1eTP j à1h i

?k j P j h i ?k tj P j h i n o ;j N 1

eEq :4T

Seavey and Liu (2008),developed a PLA synthesis simulation in Aspen Polymers (ASPEN PLUS)with the polymerization mechanism described in the following equations.The reactions (R4–R6)represent the oligomers oblation;they are esteri ?cation reactions that produce low molecular weight PLA molecules and their respective reversible reactions (hydrolysis).LA +LA ?P 2+W eR4TP n +LA ?P n

+1

+W

eR5TP n +P m ?P m +n +W

eR6T

where LA is lactic acid,W is water and,Pn is an oligomer with n acid lactic units.In the presence of the appropriate stannous catalyst,the two end groups of the linear oligomer can also react with each other forming a closed ring structure,reaction that is especially favorable for linear dimers because of the high stability of the resulting molecule (Lactide).The reaction (R7)represents this reaction and its reverse reaction (hydrolysis).P 2?C 2+W

eR7T

where P2is a linear dimer,C2is a cyclic dimer and W is water.In the polymerization steps,lactide is polymerized through ring opening and ring addition reactions in the presence of catalyst and trace amounts of water and lactic acid.This is represented in reactions (R8–R9).LA +C 2?P 3eR8TP n +C 2?P n

+2

eR9T

Due to the absence of large amounts of water and lactic acid,the Pn molecule has a high repeat unit amount,which in turn leads to a high molecular weight polymer.Seavey and Liu (2008)used the step –growth reaction kinetics model in Polymers Plus to predict the reaction rates involved in each step of the PLA process.According to Seavey and Liu (2008),the step –growth model generates a reaction network based on user-speci ?ed functional groups.In this way,the role of the user is limited to de ?ning the structure of the reactants in terms of nucleophilic and electrophilic functional groups in order to select the type of reactions to be generated by the model,which is able to ?nd all possible ways,in which,the various species can react with each other.This implemented model generates forward-and reverse-condensation

reactions (e.g.,esteri ?cation and hydrolysis)as well as subsequent rearrangement reactions (polymerization)(Seavey and Liu,2008).4.PLA biomedical applications

During the last decades,biodegradable materials have been studied extensively for medical applications,because they have advantages over nondegradable biomaterials include eliminating the need to remove implants and providing long term biocompatibility.

The most common synthetic biodegradable polymers in medical applications are the poly(α-hydroxyacid)s,including poly(glycolic acid)(PGA),poly(lactic acid)(PLA),and polydioxanone (PDS)(Middleton and Tipton,2000).Poly-lactic acid offers unique features of biodegradability,biocompatibility,thermoplastic processability and eco-friendliness that offer potential applications as commodity plastics,as in packaging,agricultural products,disposable materials and medical textile industry.Because of its favorable characteristics,PLA has been utilized as ecological material as well as surgical implant material and drug delivery systems,and also as porous scaffolds for the growth of neo-tissue (Gupta et al.,2007;Yamane and Sasai,2003).The use of poly-lactic acid in these applications is not based solely on its biodegradability nor because it is made from renewable resources.PLA is being used because it works very well and provides excellent properties at a low price (Drumright et al.,2000).Various devices have been prepared from different PLA types including degradable sutures,drug releasing microparticles,nanoparti-cles,and porous scaffolds for cellular applications.

The diversi ?cation of PLA applications is such that a single polymer may prove useful in many applications by simple modi ?cations of its physical-chemical structure.In many cases the polymer can be blended or copolymerized with other polymeric or non-polymeric components to achieve the desired behavior (Cheng et al.,2009;Gupta et al.,2007).The surface properties of materials play a critical role in determining their applications,especially for biomaterials in biocompatibility.Different surface modi ?cation strategies,such as physical,chemical,plasma,and radiation induced methods,have been employed to create desirable surface properties of PLA biomaterials.

Because biodegradable polymer implants temporarily remain in the body and disappear upon degradation,and it is no necessary a secondary operation to remove them after the defect site is repaired,they have an important application in the medical ?eld.As a ?ber the PLLA is not suitable for sutures,due to its degradation rate is very slow.On the other hand,in applications that require long retention of the strength,such as ligament and tendon reconstruction,and stents for vascular and urological surgery,PLLA ?bers are the preferred material (Durselen et al.2001).Three-dimensional porous scaffolds of PLA have been created for culturing different cell types,using in cell-based gene therapy for cardiovascular diseases;muscle tissues,bone and cartilage regeneration and other treatments of cardiovascular,neurological,and orthopedic conditions (Coutu,et al.,2009;Kellom?ki et al.,2000;Papenburg et al.2009).Osteogenic stem cells seeded on scaffolds of this material and implanted in bone defects or subcutaneously can recapitulate both developmental processes of bone formation:endochondral ossi ?cation and intramembranous ossi ?cation (Behonick et al.,2007;Caplan,2009).Due to the high strength of PLLA mesh,it is possible to create 3D structures such as trays and cages (Kinoshita et al.,2003).

An exciting application,for which the PLA offer tremendous potential,is bone ?xation devices,since the metallic ?xations have several disadvantages.Recently,biodegradable materials have been replacing metallic ones for the ?xation of fractured bones in the forms of plates,pins,screws,and wires.Since materials for bone ?xation require high strength,similar to that of bone,PLA has a large application in this ?eld.

One application of PLLA in the form of injectable microspheres is temporary ?llings in facial reconstructive surgery.PLLA microspheres have also been used as an embolic material in transcatheter arterial embolization,which is an effective method to manage arteriovenous

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?stula and malformations,massive hemorrhage,and tumors(Eppley et al.,2004;Imola and Schramm,2009).Microspheres and microcapsules have been widely applied in drug delivery systems(DDS)for the prolonged administration of a wide variety of medical agents such as contraceptives,narcotic antagonists,local anesthetics,and vaccines. DDS with peptides and proteins have also gathered much attention, since they are speci?cally effective with comparatively low doses(Tan et al.,2010).Release of drugs from these systems is based on several mechanisms that include diffusion and polymer degradation(hydroly-sis or enzymatic degradation)(Valantin et al.,2003).

5.Conclusion

According to the text reported above it is possible to observe that the biodegradable and bioabsorbable polymer synthesized from renewable resources for biomedical devices application has attracted much attention of researchers and https://www.360docs.net/doc/9f6130710.html,ctic acid,a product of industrial importance for production of several chemicals and as monomer for PLA production,can be produced by fermentation of the sucrose contained in sugarcane molasses,a by-product of sugar manufacture,and from sugarcane bagasse that is a waste available in abundance in Brazil.PLA is a well-known synthetic polymer,and it is one of the most promising biodegradable polymers used for various biomedical applications due to its biocompatibility and biodegradability.The diversi?cation of PLA applications is such that a single polymer may prove useful in many applications by simple modi?cations of its physical–chemical structure, resultant of chirality of lactic acid molecule with two asymmetric centers existing in four different forms.

Acknowledgments

The authors wish to acknowledge the?nancial support provided by FAPESP(The Scienti?c Research Foundation for the State of S?o Paulo),CNPq(National Council for Scienti?c and Technological Development)and INCT-BIOFABRIS(National Institute of Science and Technology in Biofabrication).

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药学毕业论文齐墩果酸和熊果酸保护神经的药理作用综述

齐墩果酸和熊果酸保护神经的药理作用综述 齐墩果酸和熊果酸是通过抗氧化、抗炎而产生神经保护 作用,以下是搜集整理的一篇相关论文范文,欢迎阅读参考。 齐墩果酸(oleanolicacid)和熊果酸(ursolicacid)同属 五环三萜酸类化合物,它们又是同分异构体,因此药理作用几乎 相同。现已证实齐墩果酸和熊果酸都具有抗炎、降糖、调脂、抗 肥胖、抗动脉粥样硬化药理作用[1-4],有望成为抗代谢综合征新药。代谢综合征可诱发神经系统方面的并发症,如脑中风、疼痛、糖尿病脑病、痴呆等。我国正在步入老龄社会,尤其是很多大城 市已经进入老龄社会,老年性神经精神疾病如老年痴呆、帕金森 病等发病率快速增长,而目前又缺乏安全有效、毒副作用低的防 治老年性神经精神疾病药物。齐墩果酸和熊果酸除了通过抗代谢 综合征阻滞神经系统并发症外,已有大量实验研究发现齐墩果酸 和熊果酸具有神经保护作用。本文综述齐墩果酸和熊果酸保护神 经细胞、镇痛、抗精神失常、改善学习记忆等神经精神药理方面 的研究进展,为齐墩果酸和熊果酸防治老年痴呆、帕金森病和抑 郁症的研发提供依据。 1、对离体神经细胞的保护 β淀粉样肽、过氧化氢、谷氨酸、6-羟基多巴胺等都具 有神经毒性作用,能直接损伤神经细胞引起的神经元凋亡和神经 功能障碍。齐墩果酸和熊果酸对这些神经毒素引起的离体神经细 胞损伤都有保护作用。 1.1对抗β淀粉样肽的神经毒性

PC12细胞源自大鼠髓质嗜铬细胞瘤,为神经源性细胞,具有多巴胺能神经特性,被广泛用作神经细胞体外模型,常被用来筛选神经保护药物。齐墩果酸(20、40、80mg/L)预处理PC12细胞,可浓度相关地对抗β淀粉样肽诱导乳酸脱氢酶渗漏,提高PC12细胞存活率,降低细胞凋亡率。这种神经保护作用可能与齐墩果酸促进抗凋亡基因bcl-2表达,抑制促凋亡基因bax表达有关[5].Hong等[6]报道熊果酸0.5~125μmol/L浓度相关的抑制β淀粉样肽诱导PC12细胞产生活性氧,从而减少DNA断裂和细胞凋亡。也可通过抑制上游激酶ERK1/2、p38和JNK磷酸化,阻滞核因子-κB(NF-κB)的p65亚单位核易位,抑制β淀粉样肽诱导PC12细胞表达诱生型一氧化氮合酶和环氧化酶-2,阻止神经炎症反应发生[7].Wilkinson等[8]报道熊果酸阻滞β淀粉样肽与小神经胶质细胞结合并抑制活性氧生成。用表达人CD36的中国仓鼠卵巢细胞实验,发现熊果酸浓度相关地阻滞β淀粉样肽与其受体CD36结合,浓度增至20μmol/L时作用达到峰值,最大抑制率为64%,认为熊果酸通过阻滞β淀粉样肽与CD36结合,抑制前炎性细胞因子和神经毒活性氧产生,从而阻断神经变性发生。 1.2对抗过氧化氢的神经毒性 Yu等[9]报道熊果酸0.05~2mg/L通过诱生抗氧化酶过氧化氢酶、谷胱甘肽过氧化物酶和抑制脂质过氧化反应,对抗过氧化氢损伤HEI-OC1听觉细胞。Rong等[10]报道齐墩果酸1、 10μmol/L可对抗过氧化氢损伤PC12细胞,表现为显着降低乳酸脱氢酶活性和丙二醛水平,逆转低下的线粒体膜电位、琥珀酸脱氢酶和超氧化物歧化酶活性、还原型谷胱甘肽水平,从而提高 PC12细胞存活率。Cho等[11]报道齐墩果酸通过对抗过氧化氢升高细胞内钙离子浓度和活性氧生成,抑制过氧化氢诱导大鼠皮质神经元凋亡。

熊果酸含量测定方法研究进展

熊果酸含量测定方法研究进展 (作者:___________单位: ___________邮编: ___________) 【关键词】熊果酸;含量测定方法 熊果酸(ursolie acid,UA)又名乌索酸、乌苏酸,属于三萜类化合物,广泛存在于熊果、白花蛇舌草、女贞子、乌梅等天然植物和草药中,具有抗炎、护肝、降血脂等多种生物学活性[1~4]。目前许多中药材及其制剂常选用熊果酸的含量作为其质量控制指标。本文对熊果酸含量测定方法的研究进展综述如下。 1 分光光度法 李国章等[5]建立了湘产3种苦丁茶中熊果酸含量测定的分光光度法,具体操作是取苦丁茶经索氏提取器提取后,加入5%香草醛-冰醋酸、高氯酸显色,在波长548 nm处测定吸光度,结果熊果酸在4~20 μg·ml-1浓度范围内线性关系良好,加样回收率为98.96%。罗启剑等[6]采用同样方法测定了连钱草中熊果酸含量,结果熊果酸在0~18 μg·ml-1浓度范围内线性关系良好,加样回收率为100.64%。 2 薄层扫描法

白洁等[7]采用双波长薄层扫描法测定了夏枯草中熊果酸的含量,具体操作为取夏枯草药材粗粉经95%乙醇超声提取两次,滤液用70℃水浴蒸干,残渣用石油醚浸泡两次,挥干溶剂,用95%乙醇溶解后测定。采用硅胶G板,以环己烷-氯仿-醋酸乙酯(20∶5∶8)为展开剂,用10%硫酸乙醇溶液显色,选用λS=540 nm,λR=700 nm进行双波长反射式锯齿扫描,结果熊果酸在0.314~1.570 μg范围内线性关系良好,加样回收率为99.3%。张军等[8]建立了狼疮静颗粒中熊果酸的薄层扫描法测定方法,具体操作为取狼疮静颗粒用乙醚萃取3次,合并乙醚萃取液水浴蒸干乙醚,残留物加无水乙醇-氯仿(3∶2)混合液溶解后测定,以环己烷-氯仿-醋酸乙酯-甲酸(20∶5∶8)为展开剂,用10%的硫酸乙醇液显色,以λS=520 nm,λR=700 nm进行双波长薄层扫描,结果熊果酸在0.498~3.084 μg范围内线性关系良好,加样回收率为97.91%。 3 高效液相色谱法 3.1 HPLC-UV法戚志华等[9]采用HPLC法测定了陕西女贞子中熊果酸的含量,其方法为取女贞子粉末经超声提取后采用HPLC法,选用Lichrospher C18( 4.6 mm×250 mm,5 μm)色谱柱,流动相为乙腈-甲醇-水-磷酸-三乙胺(50∶30∶20∶0.02∶0.04),流速1 ml·min-1,测定波长为205 nm,结果熊果酸在20.48~102.4 μg范围内线性关系良好,加样回收率为100.6%。梁洁等[10]采用HPLC法测定了广西产美味猕猴桃根中熊果酸的含量,具体操作为取

乌梅药材中齐墩果酸和熊果酸的高效液相色谱含量测定(一)讲解

乌梅药材中齐墩果酸和熊果酸的高效液相色谱含量 测定(一) 作者:范成杰,刘友平,陈鸿平,石宇华 【摘要】目的应用高效液相色谱(HPLC)法测定乌梅药材中齐墩果酸和熊果酸的含量,并以齐墩果酸和熊果酸为指标成分建立乌梅肉的质量标准。方法采用Hypersil ODS C18(150 mm×4.6 mm, 5 μm);甲醇-0.2%乙酸铵水溶液(83∶17)为流动相;检测波长210 nm,流速0.8 ml/min,柱温25℃。结果 齐墩果酸的线性范围为0.168~1.512 μg,r=0.999 6,回收率为98.00%(RSD=0.53%);熊果酸的线性范围为0.452~4.068 μg,r=0.999 9,回收率为97.13%(RSD=1.17%)。结论该方法简便、可靠、准确,可用于乌梅药材中 齐墩果酸和熊果酸的含量比较和乌梅肉的质量控制。 【关键词】高效液相色谱法乌梅肉齐墩果酸熊果酸 Abstract:ObjectiveTo determine the ursolic acid and oleanolic acid in the pulp of Fructus Mume by HPLC. MethodsThe ursolic acid and oleanolic acid were separated on C18 column.Methanol-0.2% Ammonium acetate solution (83∶17) was used as mobile phase and the detection wavelength was 254nm.ResultsThe linearity of ursolic acid and oleanolic acid was in the range of 0.168~1.512μg, 0.452~4.068μg, respectively; the average recoveries of ursolic acid and oleanolic acid were 98.00%(RSD=0.53%,n=5) and 97.13%(RSD=1.17%,n=5). ConclusionThe method is simple, quick and reproducible,and it can be used for the quality control of the pulp of Fructus Mume. Key words:HPLC; Pulp of Fructus Mume; Ursolic acid; Oleanolic acid 乌梅,别名酸梅、黑梅,由蔷薇科植物梅Prunus mume (Sieb.) Sieb. et Zucc.(Armeniaca mume Sieb.)的干燥近成熟果实加工而成。关于乌梅的入药方式,历代本草记载有去核和连核使用两种,现代研究证明乌梅中有效成分有机酸及水浸出物大多集中在果肉中,核含量甚少〔1〕,且核仁含大量脂肪油成分,具滑泄作用,与乌梅的固涩作用相驳;同时也有报道认为乌梅核特征明显,有利于乌梅的鉴定,而且乌梅核还含有约5%的有机酸,且去核繁琐费时 费工〔2〕,所以乌梅是否应分部位药用仍存在争议。《中国药典》Ⅰ部(2005年版)中,净乌梅和乌梅肉都有收载〔3〕。因此明确乌梅的入药方式,是建立乌梅规范的质量标准的前提。本课题组前期对乌梅各部位的化学成分进行了初步比较研究,结果表明乌梅各部位的药理作用不同,代表乌梅涩肠止泻作用的主要药用部位为乌梅果肉。本实验以齐墩果酸和熊果酸为对照品,建立了乌梅

熊果酸及五环三萜同类物的研究进展

湖南工业大学学报Journal of Hunan University of Technology Vol.23 No.5Sep.2009 第23卷 第5期2009年9月熊果酸及五环三萜同类物的研究进展 李宏杨1,刘国民1,刘 飞2,张凤琴2,李小龙2 (1. 海南大学 农学院,海南海口570228;2. 湖南工业大学包装与材料工程学院,湖南株洲412007) 摘要:五环三萜类化合物种类繁多,广泛分布在植物体中,且大多具有重要的药理活性,临床应用前景 十分诱人。随着研究的不断深入,有关五环三萜结构与活性的研究取得了大量进展,新的同类化合物不断的被发现。就熊果酸及五环三萜同类物结构与分类、在植物中的分布情况和药理作用的研究进展进行了综述。 关键词:熊果酸;五环三萜;抗肿瘤 中图分类号:Q541 文献标志码:A 文章编号:1673-9833(2009)05-0018-04 Research of Ursolic Acid and Similar Pentacyclic Triterpenoid Li Hongyang 1,Liu Guomin 1,Liu Fei 2,Zhang Fengqing 2,Li Xiaolong 2 (1. School of Agriculture ,Hainan University ,Haikou 570228,China ; 2. School of Packaging and Material Engineering ,Hunan University of Technology ,Zhuzhou Hunan 412007,China ) Abstract :Various pentacyclic triterpenoids, widely distributing in plants, have excellent pharmacological activities. The clinical application of such compounds has attracted much attentions. The research of the structure and classification of Ursolic Acid and similar pentacyclic triterpenoids and their distribution and pharmacological functions are summarized. Keywords :ursolic Acid ;pentacyclic triterpenoid ;antitumor 收稿日期:2009-08-17 基金项目:国家科技支撑计划子课题(2007BAD76B05-02)作者简介:李宏杨(1983-),男,河南信阳人,海南大学硕士研究生,主要研究方向为作物种质资源的创新与利用,E-mail :hyang896@https://www.360docs.net/doc/9f6130710.html, ;刘国民(1955-),男,湖南祁东人,海南大学教授,博士生导师,主要研究方向为作物种质资源的创新与利用,E-mail :kudingcha_no1@https://www.360docs.net/doc/9f6130710.html, 五环三萜类化合物是一类重要的天然产物,大多以游离形式或者与糖结合成苷的形式广泛存在于自然界中。熊果酸(ursolic acid )又名乌索酸、乌苏酸,属于α-香树脂烷(α-amyrin )型五环三萜类化合物。1990年,日本将熊果酸列为最有希望的癌化学预防药物之一[1]。大量研究表明,熊果酸及五环三萜同类物具有抗肿瘤、抗HIV 、抗糖尿病、抗菌、抗病毒、增强免疫功能和降血脂等多种生物学活性。近年来,国内外学者围绕熊果酸及五环三萜同类物的药理学作用、以及新五环三萜结构的发现做了大量的研究工作,取得了丰硕的成果,这些成果亦展示了五环三萜广泛的应用前景,为五环三萜的综合开发利用提供了可靠的实验依据。 1熊果酸及五环三萜同类物的结构 目前已发现的三萜类化合物多数为四环三萜和五 环三萜。五环三萜类成分在药用植物中较为常见,主要的结构类型有乌苏烷型、齐墩果烷型、羽扇豆烷型和木栓烷型等[2],见图1。 乌苏烷(ursane )型又称α-香树脂烷(α-amyrane )型,如熊果酸、积雪草酸[3]、蔷薇酸[4]、坡模酸[5]、2α-羟基乌苏酸[6];齐墩果烷(oleanane )型又称(β-香树脂烷(β-amyrane )型,如齐墩果酸、甘草酸、甘 草次酸[7]、丝石竹皂苷元[8]、蒲公英萜醇[9]、刺囊酸[10]等;羽扇豆烷(lupane )型如白桦脂醇、白桦脂酸[11]、 与分类

熊果酸抗肿瘤作用机制的研究进展

Studies in Synthetic Chemistry 合成化学研究, 2016, 4(3), 19-27 Published Online September 2016 in Hans. https://www.360docs.net/doc/9f6130710.html,/journal/ssc https://www.360docs.net/doc/9f6130710.html,/10.12677/ssc.2016.43003 文章引用: 孟艳秋, 杨丽娜, 潘洪双, 于婷婷, 张伟晨, 宁梓廷. 熊果酸抗肿瘤作用机制的研究进展[J]. 合成化学研究, Research Progress on Antitumor Action Mechanism of Ursolic Acid Yanqiu Meng, Lina Yang, Hongshuang Pan, Tingting Yu, Weichen Zhang, Ziting Ning Shenyang University of Chemical Technology, Shenyang Liaoning Received: Oct. 1st , 2016; accepted: Oct. 16th , 2016; published: Oct. 21st , 2016 Copyright ? 2016 by authors and Hans Publishers Inc. This work is licensed under the Creative Commons Attribution International License (CC BY). https://www.360docs.net/doc/9f6130710.html,/licenses/by/4.0/ Abstract Ursolic Acid is a type of pentacyclic triterpene compounds with many kinds of pharmacological ac-tivities, especially its antitumor activity. The antitumor mechanism of ursolic acid is multifaceted. In this paper, the research progress of anti-tumor mechanism of ursolic acid has been reviewed and forecasted. Keywords Ursolic Acid, Antitumor, Action Mechanism 熊果酸抗肿瘤作用机制的研究进展 孟艳秋,杨丽娜,潘洪双,于婷婷,张伟晨,宁梓廷 沈阳化工大学,辽宁 沈阳 收稿日期:2016年10月1日;录用日期:2016年10月16日;发布日期:2016年10月21日 摘 要 熊果酸是一种具有多种药理活性的五环三萜类化合物,其抗肿瘤活性尤为显著。熊果酸的抗肿瘤机制是多方面的。本文对熊果酸的抗肿瘤作用机制的研究进展进行综述并进行展望。 Open Access

熊果酸药理作用研究进展

熊果酸药理作用研究进展 ,相对分子量456 科植物毛子草的地上部分熊果酸具有广泛的 之 对致癌、促癌物有抵抗作用 多研究认为,熊果酸能通过化学预防、抗突变、细胞生长抑制和细胞毒等作用来抑制 到预防恶性肿瘤的目的。癌的发生、发展一般要经历始发突变、促癌和演变三阶段,干扰三个阶段即可达到延缓或阻止

显增加,部分细胞在

熊果酸在自然界中分布广泛,资源丰富,具有化学预防,保肝、抗肝炎,抗肿瘤、抗菌、抗病毒等多种药理活性,熊果酸药用开发景已被众多研究机构所重视,有望成为一种高效低毒的多用途新药。 【参考文献】 1 李开泉,陈武,熊筱娟,等.乌索酸的化学、药理及临床应用进展.中成药,2002, 2 4(9):709-711. 2 Muto Y,Ninomiya M,Fujiki H.Present status of research on cancer chemopre vention in Japan.Jpn J Clin Oncol,1990,20(3):219-221. 3 黄镜,孙燕.熊果酸的抗肿瘤活性.中国新药杂志,1997,6(2):101-104. 4 Niikawa M,Hayashi H,Sato T,et al.Isolation of substances from glossy prive t(Ligustrum lucidum Ait)inhibiting the mutagenicity of benzo(α)preene in bacteri a.Mutat Res,1993,319(1):1-4. 5 Young HS,Chung HY,Lee CK,et al.Ursolic acid inhibits aflatoxin B1-induced mutagenicity in a Salmonella assay system.Biol Pharm Bull,1994,17(7):990-99 3. 6 Huang MT,Ho CT,Wang ZY,et al.Inhibition of skin tumorigenesis by rosema ry and its constituents carnosol and ursolic acid.Cancer Res,1994,54(3):701-70 5. 7 Ohigashi H,Takamura H,Koshimizu K,et al.Search for possible an-titumor p romoters by inhibition of12-O-tetrade-canoylphorbol-13-acetate-induced Epstein-Barr v irus activation;ursolic acid and oleannolic acid from an anti-inflammatory Chinese m edicnal plant,Glechoma hederaceae L.Cancer Lett,1986,30(2):143-148. 8 Ames BN.Dietary carcinogens and anticarcinogens.Science,1983,221:1256-12 58. 9 Balanehru S,Nagarajan B.Protective effect of oleanolic acid and urso-lic acid against lipid peroxidation.Biochem Int,1991,24(5):981-984.

不同产地及外观形态夏枯草中齐墩果酸和熊果酸的含量比较

不同产地及外观形态夏枯草中齐墩果酸 和熊果酸的含量比较 (作者:___________单位: ___________邮编: ___________) 【摘要】目的比较不同产地、长度、色泽的夏枯草中齐墩果酸和熊果酸的含量,为更全面地控制夏枯草的质量提供依据。方法采用高效液相色谱法,以Shim Pack C18为色谱柱,乙腈甲醇水乙酸铵(体积比68∶16∶16∶0.5)为流动相,检测波长为215 nm,流速为0.8 mL/min。结果与结论不同产地夏枯草中齐墩果酸和熊果酸的含量差异较大,果穗短者两者含量高于果穗长者,紫红色果穗者两者含量高于棕色果穗。 【关键词】夏枯草产地果穗齐墩果酸熊果酸 Abstract:Objective To compare the contents of oleanolic acid and ursolic acid in Prunella vulgaris with different appearances and from different provenances,in order to control the quality of Prunella vulgaris.Methods Samples were analyzed on a Shim Pack C18 column. The mobile phase consisted of acetonitrile methol water ammonium acetate (68∶16∶16∶0.5)

under a flow rate of 0.8 mL·min-1. The detection wavelength was set at 215 nm.Results and Conclusions There were large differences in contents of oleanolic acid and ursolic acid among Prunella vulgaris with different provenances and appearances, higher in Prunella vulgaris with short and mauve ears. This method was suitable for the quality control of Prunella vulgaris. Key words:Prunella vulgaris;oleanolic acid;ursolic acid 夏枯草Prunella vulgaris为常用中药,以干燥果穗或全草入药,主要用于治疗目赤肿痛、头痛眩晕、瘰疬瘿瘤、乳痈肿痛、高血压等[1]。夏枯草中含有三萜及苷类、苯丙素类、黄酮类等多种化学成分,其中齐墩果酸和熊果酸是主要活性成分[2,3]。目前文献报道有采用衍生化气相色谱法、毛细管胶束电动色谱法、高效液相色谱法等方法评价夏枯草的质量[4-6],但对于不同产地、长度、色泽的夏枯草中这两种三萜酸的含量比较还未见报道。本文以高效液相色谱法测定并比较不同产地、长度、色泽夏枯草样品中齐墩果酸及熊果酸的含量,旨在为更全面控制夏枯草的内在质量提供依据。 1 仪器与试药 Agilent 1100高效液相色谱仪:包括G1313A自动进样器,Agilent ChemStations数据处理软件,美国安捷伦科技有限公司;齐墩果酸对照品、熊果酸对照品:中国药品生物制品检定所,批号分别为110709200304、110742200516;乙腈:色谱纯,美国TEDIA公司;甲醇:分析纯及色谱纯,江苏汉邦科技有限公司;石油醚、乙酸铵:

熊果酸的功效与作用

熊果酸是由天然植物中的一种三萜类化合物而来,具特殊的气味,是存在于天然植物中的一种五环三萜类化合物。那么熊果酸具体有哪些的作用与功效呢?下边不妨一起来简单了解一下吧。 一、熊果酸的作用及功效 据临床医学表示,熊果酸中有的有益分子,非常显著而迅速的可以降低谷丙转氨酶、血清转氨酶等,对于消退小儿黄疽以及增进食欲等方面都有很好的促进,而对于抗纤维化和恢复肝功能症状,效果也非常的明显,而且还特别的稳定。熊果酸还具备有非常明显的抗氧化功效,这也使得它成为医药及化妆品方面的常备原料,例如医药方面对于肝部的治疗非常有益,能够保护并稳定稳定肝细胞膜、细胞器,从而使输出、运输等功能相继慢慢的恢复,在化妆品方面,由于熊果酸有很好的抗氧化作用,能使肌肤具有抵抗力,与此同时还有效淡化皱纹、修肌肤等皮肤难题。且熊果酸其实还是一味天然的保湿剂,大病可以调理,小病可以医治,又给人们带来不少的惊喜。

二、含量测定标准 1、色谱条件: 硅胶G薄层板;环己烷-氯仿-乙酸乙酯(20:5:8)为展开剂,上行展开;展距12~18cm;5%硫酸乙醇溶液,110℃加热5min显色。 2、样品溶液的制备: 精密称取栀子粉碎样品20g (炒栀子按得率折合后称取),置索氏提取器内,加乙醚300ml回流提取至无色,回收溶剂至干,残留物加石油醚浸泡2次,每次15ml,约浸泡2min,倾去石油醚,用无水乙醇-乙醚(2:3)混合液微热使溶解并定容于5ml量瓶中,作为样品溶液。 3、对照品溶液的配制: 精密称取熊果酸对照品适量,加无水乙醇:乙醇(3:2)的混合溶液制成每毫升含1mg的溶液,作为对照品溶液。 4、测定: 准确吸取样品溶液及对照品溶液2μl,点于同一薄层板上。按上述色谱条件展开,显色。照薄层扫描法扫描,λS=520nm,λR=700nm;双波长反射法锯齿

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齐墩果酸与熊果酸结构修饰物的药理活性和构效关系研究进展 刘丹1,2 孟艳秋23 赵娟2 (1天津大学药物科学与技术学院 天津 300072; 2沈阳化工学院制药工程教研室 沈阳 110142) 刘丹 女,35岁,副教授,主要从事天然活性成分的结构修饰和医药中间体的合成工作。 3联系人,E 2mail :myq6581@https://www.360docs.net/doc/9f6130710.html, 辽宁省自然科学基金资助项目(20042009) 2005-12-12收稿,2006-08-15收稿 摘 要 齐墩果酸(OA )和熊果酸(UA )均属于五环三萜类化合物,广泛存在于自然界中,具有多种显著的 生物活性。本文综述了近年来齐墩果酸及熊果酸结构修饰物的药理活性和构效关系的研究进展。 关键词 齐墩果酸 熊果酸 结构修饰 药理活性 R ecent Advance in the Study on Derivatives of Oleanolic Acid and U rsolic Acid Liu Dan 1,2,Meng Y anqiu 23,Zhao Juan 2(1C ollege of Pharmaceuticals &Biotechnology ,T ianjin University ,T ianjin 300072;2Faculty of Pharmaceutical Engineering ,Shenyang Institute of Chemical T echnology ,Shenyang 110142) Abstract Oleanolic acid and urs olic acid belong to triterpene acids which having numerous pharmacological activities and widely presenting in food ,medicinal herbs and other plants.Here a brief introduction of the recent progresses on pharmacological activities and the structure-activity relationship of derivatives of olean olic acid and urs olic acid are given out. K ey w ords Oleanolic acid ,Urs olic acid ,M odification ,Pharmacological activities 齐墩果酸(oleanolic acid ,OA ,1)和熊果酸(urs olic acid ,UA ,2)为结构类似物,均属于五环三萜类化合物,在自然界分布十分广泛,且具有多种生物活性。为了寻找高效低毒的衍生物,需对齐墩果酸和熊果酸的作用机制进行深入的研究;通过对32位羟基,C 122C 13位双键和282位羧基等官能团的结构修饰合成了一系列衍生物,进行了相关的药理活性测试,并与母体进行比较,获得了相应的构效关系。本文将就齐墩果酸及熊果酸结构修饰物的药理活性和构效关系研究进展进行综述。 1  齐墩果酸及熊果酸化学及药理活性简介 齐墩果酸(C 30H 48O 3)属于β-香树脂醇型五环三萜类化合物,据不完全统计,它以游离形式或与糖结合的形式存在于大约60个科190种植物中[1],具有保肝[2,3]、消炎[4]、降糖[5]、抗HI V [6,7]和抗肿瘤[8~10]等药理作用。 熊果酸(C 30H 48O 3)为α-香树脂醇型五环三萜类化合物,以游离形式或与糖结合的形式存在于大约

熊果酸

打开的谱图文件:D:\10\熊果酸标准品3(00001).hw ───────────────────────────序号 保留时间 名称 峰面积% 峰面积 ─────────────────────────── 1 0.20 2 0.00464 3 118 2 0.23 3 0.001742 44 3 0.278 0.002292 58 4 0.444 0.009194 233 5 0.652 0.006404 163 6 0.922 0.006128 156 7 1.150 0.005266 134 8 1.199 0.002263 57 9 1.236 0.002975 76 10 1.453 0.009436 240 11 1.652 0.0075 190 12 1.803 0.001693 43 13 2.070 1.414 35901 14 2.659 0.09665 2454 15 2.777 0.1092 2773 16 3.084 1.454 36908 17 3.726 1.346 34185 18 4.277 0.2177 5529 19 4.675 0.4557 11571 20 4.886 0.322 8176 21 5.498 93.84 2382895 22 7.284 0.02985 758 23 7.588 0.006965 177 24 7.853 0.003855 98 25 8.058 0.01011 257 26 8.294 0.0007985 20 27 8.404 0.002138 54 28 8.594 0.00232 59 29 8.920 0.006411 163 30 9.097 0.003013 77 31 9.357 0.005584 142

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熊果酸及五环三萜同类物的研究进展 李宏杨1,刘国民1,刘飞2,张凤琴2,李小龙2 (1. 海南大学农学院,海南海口570228 ;2. 湖南工业大学包装与材料工程学院,湖 南株洲412007) 摘要:五环三萜类化合物种类繁多,广泛分布在植物体中,且大多具有重要的药理活性,临床应用前景十分诱人。随着研究的不断深入,有关五环三萜结构与活性的研究取得了大量进展,新的同类化合物不断的被发现。就熊果酸及五环三萜同类物结构与分类、在植物中的分布情况和药理作用的研究进展进行了综述。 关键词:熊果酸;五环三萜;抗肿瘤 五环三萜类化合物是一类重要的天然产物,大多以游离形式或者与糖结合成苷的形式广泛存在于自然界中。熊果酸(ursolic acid) 又名乌索酸、乌苏酸,属于oc 一香树脂烷(r,-amyrin) 型五环三萜类化合物。1990 年,日本将熊果酸列为最有希望的癌化学预防药物之一。大量研究表明,熊果酸及五环三萜同类物具有抗肿瘤、抗HIV、抗糖尿病、抗菌、抗病毒、增强 免疫功能和降血脂等多种生物学活性。近年来,国内外学者围绕熊果酸及五环三萜同类物的药理学作用、以及新五环三萜结构的发现做了大量的研究工作,取得了丰硕的成果,这些成果亦展示了五环三萜广泛的应用前景,为五环三萜的综合开发利用提供了可靠的实验依据。 1 熊果酸及五环三萜同类物的结构与分类 目前已发现的三萜类化合物多数为四环三萜和五环三萜。五环三萜类成分在药用植物中较为常见,主要的结构类型有乌苏烷型、齐墩果烷型、羽扇豆烷型和木栓烷型等,见图1。 乌苏烷(Ill'Sane) 型又称一香树脂烷(r,-amyrane) 型,如熊果酸、积雪草酸、蔷薇酸引、坡模酸I 、2 一羟基乌苏酸:齐墩果烷(oleanane) 型又称( 口一香树脂烷(B-amyrane) 型,如齐墩果酸、甘草酸、甘草次酸、丝石竹皂苷元引、蒲公英萜醇、刺囊酸等;羽扇豆烷(1upane)型如白桦脂醇、白桦脂酸n”羽扇豆醇、乙酸羽扇豆醇酯ml等;木栓烷(friedeiane) 型如木栓酮㈣、雷公藤红素、demethylzeylasteral 、salaspermic acid 、2,3 — dihydroxy-friedel-6 ,9(1 1) 一en 一29-oic acid 等。 2 熊果酸及五环三萜同类物在植物中的分布 据不完全统计,在自然界已有34科108种植物中能分离得到熊果酸,主要分布在女贞子、山楂、珍珠菜、夏枯草、车前草、甘草、连翘和苦丁茶等药用植物中。齐墩果酸是一种齐墩果烷型五环三萜类化合物,广泛分布于约60 科190种植物中,如:青叶胆全草、白花蛇舌草、女贞果实等,以游离形式或与糖结合成苷存在。就冬青科苦丁茶而言,目前发现含量 最丰富的五环三萜类化合物是熊果酸和齐墩果酸,主要存在于苦丁茶冬青、大叶冬青的枸骨嫩芽和功能叶之中。除此之外,冬青科苦丁茶中尚含有若干种含量较低的其它五环三萜类化合物。人们在大叶冬青中分离鉴定了 1 3 种新型三萜皂苷和7 种三萜苷元;在苦丁茶冬青

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三维介孔材料SBA-16的制备 分别称取12 g F108和31.44 g硫酸钾放入500 mL烧杯中,加入360 g浓度为2 M的盐酸。在室温下(25 °C)搅拌4 h,使表面活性剂全部溶解并且分散均匀后,将温度升至38 °C。待恒温后,在剧烈搅拌下,逐滴加入25.2 g正硅酸乙酯(TEOS),连续搅拌20 min后停止。静置保持反应物24 h,整个过程维持38 °C 不变。所得白色粉末,通过离心进行收集(转速5000 rpm),用去离子水洗涤6次,并在烘箱中40 °C干燥。表面活性剂在500 °C空气中焙烧5 h去除,升温速度控制在2 °C /min。 二维介孔二氧化硅材料SBA-15的制备 室温下,将1 g P123和2.24 g KCl溶于30 g 2 M的盐酸中,当搅拌至均一溶液后,逐滴加入2.08 g正硅酸乙酯(TEOS),并强烈搅拌30 min。静置24 h 后,把所得混合物转移至带聚四氟乙烯衬套的不锈钢反应釜中,100 °C晶化24 h。自然冷却后,经抽滤,反复洗涤,在烘箱中过夜烘干。 三维介孔二氧化硅材料SBA-16的制备 在45 °C下,将4.0 g F127和8.0 g浓盐酸(37 wt%)溶于192 g蒸馏水中。在搅拌均一后,加入12.0 g 正丁醇,并强烈搅拌1 h。逐滴加入18 g正硅酸乙酯(TEOS)后,在相同温度下搅拌24 h。将所得混合物转移至带聚四氟乙烯衬套的不锈钢反应釜中,100°C晶化24 h。自然冷却,经抽滤,反复洗涤,所得粉末样品在烘箱中过夜烘干。 MCM-41的合成 将4.38 g CTAB加入到含1.10 g NaOH的200 g蒸馏水中。室温搅拌使其完全溶解,逐滴加入5.21 g TEOS,并继续搅拌24 h。将混合物转移至带有聚四氟乙烯内衬的反应釜中,在110 °C条件下晶化24 h。所得产物抽滤后,用蒸馏水反复冲洗直至滤液呈中性,将产物干燥。 介孔二氧化硅分子筛KIT-6的制备

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2010年第卷第期 137[收稿日期]2010-05-14 [作者简介]刘柯彤(1988-),陕西榆林人,陕西理工学院化学工程与工艺专业2008级本科生。摘要:综述了近年来熊果酸生物活性的研究进展,重点讨论了其研究热点,展望了其今后的发展趋势。 关键词:熊果酸;生物活性;研究热点 中图分类号:O624 文献标识码:A doi :10.3969/j.issn.1007-7871.2010.07.002 熊果酸的生物活性及其研究热点 刘柯彤,陶亮亮,马雄,刘军海 (陕西理工学院化学与环境科学学院,陕西汉中723001) 0前言熊果酸(Ursolic Acid ,UA ),又名乌索酸、乌苏酸,属α-香树脂醇型五环三萜类化合物。纯净的熊果酸为白色针状晶体,熔点为285~287℃,易溶于二氧六环吡啶,可溶于甲醇、乙醇,微溶于丙酮、苯、氯仿和乙醚。在自然界中熊果酸主要分布在女贞子、山楂、夏枯草、车前草和苦丁茶等多种植物中[1,2]。近年来,有关熊果酸的提取已经成为天然产物加工领域的研究热点之一;随着对熊果酸生物活性研究的深入,其在医药、食品、保健和化妆品等领域获得了广泛的应用。本文综述了熊果酸的提取工艺及其生物活性的研究进展,重点讨论了研究的热点问题及发展趋势,以期为熊果酸进一步的开发利用提供参考。1熊果酸的生物活性熊果酸具有广泛的生物活性,尤其在抗肿瘤、抗氧化、抗菌抗病毒、保肝和美容护肤等方面的作用显著,值得重视。1.1抗肿瘤作用研究发现,熊果酸具有抗致癌、抗促癌、诱导F9畸胎瘤细胞分化和抗肿瘤血管形成的作用。其主要通过以下几方面进行作用:熊果酸能抗突变、抑制癌变的启动、能直接杀伤肿瘤细胞,具有肿瘤逆转作用及抗侵袭性、诱导肿瘤细胞凋亡和抑制肿瘤血管形成,从而抑制癌变的形成;并且对多种肿瘤细胞体内、外均有抑制作用,并可 以减少放疗、化疗之后对造血系统的损害[3]。熊果酸对结肠癌、黑色素瘤和胃癌等多种细胞系具有抑制作用,并诱导其凋亡,其机制可能是通过影响细胞周期及癌相关基因的表达而实现的[4]。于丽波等研究发现熊果酸可明显抑制卵巢癌细胞生长,并诱导细胞凋亡,其主要机制与调节Bcl-2和Bax 的蛋白表达有关[5]。刘琼等研究表明, 熊果酸具有抑制恶性胶质瘤裸鼠移植瘤生长的作用,其机制可能与下调ERK1、C -Jun 、C -Myc 、CyclinD1表达有关[6]。 1.2抗氧化作用 氧化作用是造成人类衰老现象的重要原因之一,在防止人体内不良胆固醇(LDL )的氧化,保持血管的年轻化方面,熊果酸扮演着重要角色。 熊果酸具有明显的抗氧化功能,因而被广泛 地用作医药和化妆品原料。抗氧化作用对人体抗 衰老和皮肤祛斑、祛色素、美容都有积极作用。 对于熊果酸的抗氧化作用有人曾作过研究,如卢静等采用邻苯三酚自氧化法,Feton 体系法测定熊果酸对超氧阴离子和羟自由基的清除能力,从而 探究熊果酸的抗氧化性能。结果表明熊果酸对超 氧阴离子和羟自由基有明显的清除作用,对超氧 阴离子的最高清除率可达88.42%,但是清除作用弱于同浓度下的VC 。熊果酸对羟自由基的清除作用最高可达86.35%,并且强于同浓度下的甘露醇,具有明显的抗氧化性[7]。王建梅等研究发现,熊果酸有保护糖尿病大鼠血管损伤的作用,机制可能 Surveys &Reviews 综述与述评 11

熊果酸的研究进展

作者:肖坤福郑云法刘成左张春牛 【关键词】熊果酸;,,,检测方法;,,,提取方法;,,,动物实验;,,,临床研究熊果酸是广泛存在于白花蛇舌草、女贞子、乌梅、夏枯草等天然植物中的一种五环三萜类化合物,有研究表明熊果酸具有镇静、抗炎、抗菌、抗糖尿病、降血糖等多种生物学效应,早在1996年,日本学者神藏美枝子等人从杜鹃花科越桔属植物越桔叶中提取了具有较高熊果酸浓度的熊果酸产品,产品中除含有25%的熊果酸外,尚含有大量的熊果酸衍生物、熊果苷和其它三萜类化合物等,具有多种活性成分,用于增强机体免疫力、预防心血管系统疾病、稳定肝功能等。现在人们对其研究越来越多,并在很多方面取得了可喜的研究进展。 1 提取方法 对三萜类化合物的分离提纯是其研究起点,没有较好的提取工艺,就更谈不上对其进一步研究。近年来,许多科研工作者在这方面做出了突出的贡献。有些科研工作者[1~5],通过正交实验确定85%~95%的乙醇提取熊果酸效果最佳。崔星明等[6]采用超临界流体萃取得到的芦笋提取物,用甲醇溶解,采用液相色谱-质谱联用仪检测,得到了56个组分。发现有保留时间和熊果酸基本一致的峰。其质谱分子离子峰和特征碎片峰都与熊果酸的一致,确定该化合物为熊果酸。 2 检测方法 在检测方法方面,有不少科研工作者对其进行了较深入的研究。熊慧敏[7]全面地论证了薄层层析-双波长扫描法测定大山楂咀嚼片中熊果酸含量的检测限的线性范围可行性,并考查了此方法的测定熊果酸的稳定性和重复性,从而证明薄层层析-双波长扫描法测定熊果酸精密度、稳定性、重现性、回收率均都达有关规定的要求,本方法操作简单方便,结果可靠,可作为检验产品质量的一个快速而实用的定量方法。朱玉琴等[8]在采用薄层扫描检测保驾胶囊中熊果酸的含量时首次对显色剂进行了改进,并验证了醋酸-浓硫酸 (9∶1)比10%硫酸乙醇显色要好,检测限低等优点。与此同时,杨云等[9]在采用薄层层析检测牙周康泰胶囊熊果酸的含量验证了10%磷钼酸乙醇液比10%硫酸乙醇显色要好。 罗启剑等[10]采用分光光度法测定连钱草中熊果酸含量。郭艳玲等[11]和陈志强[12]采用薄层扫描法分别测定了补肾颗粒和消食贴中熊果酸含量,方法简便、快速、准确,可作为该产品的质量控制方法。 周静等[13]探求用毛细管气相色谱法测定女贞子中齐墩果酸和熊果酸含量。取女贞子氯仿提取液自然挥发干,甲醇溶解经甲酯化后,进样分析。色谱条件:hp-1毛细管柱(25 cm×0.32 mm,0.52 μm),柱温280℃,氮气为载气,氢火焰检测器。分析结果表明熊果酸的线性良好,回收率为99.8%±2.1%。所建立的气相色谱法可以作为女贞子药材的质量检测方法。 施慧君等[14]采用hplc法测定知柏地黄冲剂中熊果酸的含量。选用ods-c:色谱柱,流动相:甲醇-水(99∶1),磷酸调ph 2.5,检测波长:206 nm,流速:1.2 ml/min,柱温25℃的条件下,熊果酸线性关系良好(r=0.999 8) 平均回收率达98.7%(rsd=0.66%)。罗晓清等[15]采用rp-hplc法测定石精叶中熊果酸含量,色谱柱为zorbax ods柱,用甲醇(1%),醋酸水溶液(88∶12)为流动相。检测波长为215nm。结果熊果酸和齐墩果酸的平均收率分别为98.5%、97.6%(n=3)。rsd分别为1.62%,1.89%(n=3)。方法准确、灵教、快速,可作为石抽叶药材的质量检测方法之一。 杨书良等[16]采用高效液相色谱法从影响熊果酸测定的各个方面(例如:粒度、煎煮次数、溶媒量、提取时间等)进行测定和和正交分析,从而论证了它比薄层层析法更精确、更可靠、灵敏度更高,重现性更好。鞠建华等[17],也采用高效液相色谱测定熊果酸含量,但他在前人的基础上调节流动相的比例和加入改性剂乙酸胺,验证了此改进方法可以使熊果酸和它的同分异构体齐墩果酸达到基线分离,并使基线平稳、峰型和分离效果较佳。鄢立新等

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