磁性微球的制備及其生物分離應(yīng)用

1、Chapter 3 Chemical Structure and Metabolism第三章 化學(xué)結(jié)構(gòu)與藥物代謝Section 1 Introductionl The physicochemical properties of drugs that predispose (使偏向于) them to good absorption, such as lipophilicity (親脂性) , are impediment(妨礙) to their elimination. l As a consequence, the elimination of drugs normally require

2、s their conversion into water soluble compounds by a process of metabolism, which enables excretion via urine or faeces(排泄物). Metabolisml Metabolism is often the major factor defining the pharmacokinetics of drugs, which in turn can influence the efficacy and side-effect profile of these compounds.

3、l The chemical nature and means of identification of these biotransformations have been well known for many years, but in recent years major advances have been made in the understanding of the enzymes responsible for the metabolic pathways. Section 2 Enzymes for Drug Metabolism （第二節(jié) 藥物代謝的酶） l The dr

4、ug metabolizing enzymes are usually classified by the reactions they catalyse, as either Phase I or Phase II. Phase I Biotransformationl Phase I reactions introduce, or otherwise produce, a functional group (e.g. OH, -SH, -NH2, -COOH) into the molecule. l These reaction include hydrolysis (水解) , red

5、uction (還原) and oxidation (氧化) and are performed by a wide range of enzymes. l Often these Phase I reactions precede Phase II biotransformations.l 第I相生物轉(zhuǎn)化主要是官能團反應(yīng)，包括對藥物分子的氧化、還原和羥化等，在藥物分子中引入或暴露極性基團，如羥基、羧基、巰基和氨基。Phase II Biotransformationl Phase II reactions involve the conjugation (軛合) on a suitable

6、chemical group of the molecule (parent compound or metabolite) and many drugs contain suitable functional groups without recourse (依賴) to Phase I metabolism. l Phase II reactions include conjugation with glucuronic (葡萄糖醛酸) acid, sulfate, glutathione (谷光苷肽) or amino acids (e.g. glycine (甘氨酸), taurine

7、 (牛磺酸), glutamine(谷氨酰胺), all of which increase the water solubility of the molecule. l Conjugation reactions, such as N-acetylation of amines and N-, O- and S-methylation, generally result in more lipophilic products. 1. Cytochrome P-450 enzyme system（CYP-450）(細(xì)胞色素P-450酶系)l Cytochrome P-450 enzyme s

8、ystem (CYP-450) are a group of nonspecific enzymes (Heme-coupled monooxygenases) in liver microsomes. In a another word, CYP 450 is a liver homogenate (勻漿) fraction derived from smooth endoplasmic reticulum(光滑內(nèi)質(zhì)網(wǎng)). l CYP-450是一組鐵原卟啉偶聯(lián)單加氧酶，位于肝微粒體中，是主要的藥物代謝酶系。l CYP-450屬于體內(nèi)的氧化還原酶，主要進行氧化反應(yīng)，需要NADPH和氧分子共同參

9、與。也能進行還原反應(yīng),將含偶氮和硝基還原成芳香伯胺。 2. Reduction enzyme system(還原酶系)l CYP-450酶系（CYP-450）l 醛酮還原酶(ketoreductase)：屬于氧化還原酶。需要NADPH或NADP作為輔酶。l 谷胱甘肽氧化還原酶(glutathione oxido- reductase) l 醌還原酶3. Other oxidative enzymes l Flavin monooxygenase (黃素單加氧酶)l Monoamine oxidase(單胺氧化酶)l Aldehyde oxidase (醛氧化酶)Flavin Monooxyge

10、nase (FMO) (黃素單加氧酶) l The FMO are microsomal enzymes and many of the reactions they catalyse can also be catalysed by cytochrome P450. l The commonest FMO reaction is the oxidation of nucleophilic tertiary amines to N-oxides, although primary and secondary amines and several sulfur-containing drugs

11、are also substrates. l FMO通常對N和S雜原子進行氧化，而不發(fā)生雜原子的脫烷基化反應(yīng)。 Monoamine oxidase (MAO)(單胺氧化酶)l MAO is involved in the oxidative deamination of amines. l Substrates include a number of endogenous(內(nèi)源的) amines. Aldehyde oxidase l Aldehyde oxidase can oxidize a number of substituted pyrroles(吡咯), pyridines(吡啶)

12、, primidines and purines (嘌呤).l And its substrates include methotrexate (甲氨蝶呤), quinidine (奎尼定) and cyclophosphamide (環(huán)磷酰胺). Hydrolysis Esterase (酯酶) l In general, esters and amides are hydrolyzed by enzymes in the blood, liver microsomes, kidneys, and other tissues. l Esters are rapidly hydrolyzed

13、by esterases. l 水解酶位于血漿、肝、腎和腸中，參與酯和酰胺的水解。但酰胺較穩(wěn)定而難水解。Esterasesl Acetylcholinesterase(乙酰膽堿酯酶) l cholinesterase (pseudocholinesterase擬膽堿酯酶) l Arylesterase(芳基酯酶)l Liver microsomal esterases(肝微粒體酯酶)l Other unclassified liver esterases 環(huán)氧化物酶等。 Table 1 The drug metabolizing EnzymesEnzymePhaseReactionLocali

14、cationAlcohol(醇) dehydrogenaseIOxidationCytosol(胞質(zhì)溶膠)Aldehyde (醛) dehydrogenaseIOxidationMitochondria, CytosolAldehyde oxidase IOxidationCytosolCarbonyl (羰基) reductaseIReduction and OxidationCytosolCarboxylesterase (酯酶)IHydrolysisMicrosomes, CytosolCytochrome P450IOxidation or ReductionMicrosomesDia

15、mine oxidase (氧化酶)IOxidationMitochondria（線粒體）Epoxide (環(huán)氧化物) hydrolaseIHydrolysisMicrosomes, CytosolFlavin(黃素) Monooxygenase IOxidationMicrosomesTable 1 The drug metabolizing EnzymesGlucuronyl transferaseIIConjugationMicrosomesGlutathione S-transferaseII or IConjugation or reductionCytosol, Microsome

16、sMonoamine (單胺) oxidase IOxidationMitochondriaN-acetyl transferaseIIConjugationMitochondria, CytosolPeptidase (肽酶)IHydrolysisBlood, lysosomes(溶酶體）Quinone (醌) oxidoreductase IReductionCytosolSulfotransferase (硫轉(zhuǎn)移酶)IIConjugationCytosolXanthine (黃嘌呤) oxidaseIOxidationCytosolSection 3 Phase I Biotransfo

17、rmation l 1. Oxidationsl 2. Reductionsl 3. Dehalogenationl 4. Hydrolysis1. Oxidationsl I. Oxidation of compounds containing Cl II. Oxidation of compounds containing Nl III. O-dealkylation of ethers l IV. Oxidation of compounds containing Sl V. Oxidation of alcohol and aldehydesI. Oxidation of compou

18、nds containing Cl A. Aromatic hydroxylationl B. Olefinic oxidationl C. Aliphatic and alicyclic hydroxylationsA. Aromatic(芳香族的) Hydroxylation RROHHRHH-OROHHROHROHOHSGOHRXOHRrearrangedH2OGSHepoxide hydrase glutathione S-transferases intracellular macromolecules(DNA,RNA) XCYP-450toxicitymain Characteri

19、stics of aromatic hydroxylation (1) l 1. For monosubstituted benzene compounds, para hydroxylation usually predominates, with some ortho product being formed. l 2. In cases where there is more than one phenyl ring, only one ring is usually hydroxylated. HNNHOOHNNHOOOHPhenytoin(苯妥英)NNOOC4H9NNOOC4H9OH

20、Phenylbutazone(保泰松)High potencyLess toxicityCharacteristics of aromatic hydroxylation (2)l 3. The position of hydroxylation can often be influenced by the type of substituents on the ring according to the theories of aromatic electrophilic substitution. Electrondonating substituents enhance, whereas

21、 electronwith-drawing substituents reduce or prevent hydroxylation. l 4. Steric factors must also be considered, because oxidation usually occurs at the least hindered position. ClClNHHNNClonidine(可樂定)Probenecid(丙磺舒)SO2N（CH2CH2CH3）2HOOCNSRClCH2CH2CH2NMe2R=HR=OHChlorpromazine（氯丙嗪)OOHOHSGOHNaphthalene

22、（萘環(huán))l Naphthalene and halobenzenes afford 1,2-dihydrodiols and glutathione conjugates because of a stable epoxide.Polycyclic aromatic hydrocarbons OHOOHHOOHORNAHOHONHHORNA(carcinogenesis)Attention lHowever, it should be pointed out that where other competitive pathways of biotransformation exist, th

23、e importance of arene oxide formation can be diminished. lMore vulnerable substituents will be metabolized preferentially, thus facilitating excretion. B. Olefinic(烯烴) Oxidation l Olefinic oxidation is analogous to aromatic oxidation, involving an epoxide intermediate. l Stable epoxides and vicinal

24、dihydrodiols have been isolated. Carbamazepine（卡馬西平）NCONH2NCONH2NCONH2OHOOHCYP-450epoxide hydraseAflatoxin B1（黃曲霉素）OOOOCH3OOOOOOCH3OOOOOOCH3OOOHODNADNAHHHH(carcinogenesis)(aflatoxin B1) (epoxides)C. Aliphafic (脂肪族) and Alicyclic (脂環(huán)族) Hydroxylations CH2CH2CHCH2CYP-450.CYP-450CYP-450CHCH2OHCHCH2CYP-4

25、50priorityAliphafic and Alicyclic Hydroxylationsl Alkyl side chainsl Carbons adjacent to SP2 carbonl Alicyclic (脂環(huán)族)Sodium Valproate（丙戊酸鈉）CH3CH2CH2CHCOONaC3H7-nHOCH2CH2CH2CHCOONaC3H7-nCH3CHCH2CHCOONaC3H7-nHO-Oxidation-1-OxidationHOOCCH2CH2CHCOONaC3H7-nAlkyl side chainsAmobarbitar（異戊巴比妥）NHNHOOC2H5CHC

26、H2CH2OCH3CH3NHNHOOC2H5CCH2CH2OCH3CH3HOIbuprofen（布洛芬） CHCH2CHCH3COOHCH3CH3CHCH2CHCH3COOHCH3HOCH2C-CH2CHCH3COOHCH3CH3HOOxidation of C adjacent to SP2 carbonl The methylene groups adjacent to SP2 carbon generally are activated position, e.g., to a carbonyl; to a double bond (allyl,烯丙基); to a phenyl rin

27、g (benzyl). l They are oxidized to the hydroxymethyl derivative by CYP450.Diazepam（地西泮）NNCH3OClNNCH3OClHOHTemazepam替馬西泮 to a carbonylTolbutamide（甲苯磺丁脲）CH3SO2NHCONHC4H9CH2OHSO2NHCONHC4H9COOHSO2NHCONHC4H9benzylToluene CH3COOHbenzylPentazocin（鎮(zhèn)痛新）HOCH3CH3NCH2CH=CCH3CH3HOCH3CH3NCH2CH=CCH2OHCH3HOCH3CH3NC

28、H2CH=CCH3CH2OHallylTetralin (1,2,3,4-tetranaphthalene)OHOH+AlicyclicbenzylAcetohexamide（醋磺己脲）CH3COSO2NHCONHHCH3COSO2NHCONHHHOHAlicyclicII. Oxidation of compounds containing N N CHHN CHHN CHHN CHHON CHN CHN CHOHNHO+carbinolamine+-HCYP450. .A. N-Dealkylation B. N-OxidationA. N- DealkylationlThe mechan

29、ism for the N-dealkylation reaction is oxidation of the -carbon, generating an unstable carbinolamine（甲醇胺）that collapses to yield the N-dealkylated substrate and the carbonyl derivative of the substituent. Classification of N-DealkylationPropranol（普萘洛爾）OHONHOHONHOHOHONHOHOCOOHOHOHONH2OHOCHO+ONH2+Amp

30、hetamine（苯丙胺）NH2OCharacteristics of N-Dealkylationl 1. Some of the N substituents removed by oxidative dealkylation are methyl, ethyl, n-propyl, isopropyl, n-butyl, allyl, benzyl, and others having an -H. l 2. Substituents that are more resistant to dealkylation include the tert-butyl (no -H) and th

31、e cyclopropylmethyl. l 3. In general, tertiary amines are dealkylated to secondary amines faster than secondary amines are dealkylated to primary amines. Katamine（氯胺酮）NHCH3ClONH2ClOLidocaine（利多卡因）NHCOCH2NCH3CH3C2H5C2H5NHCOCH2NHC2H5CH3CH3easilytoxicityImipramine（丙咪嗪 ）Desipramine 地昔帕明N(CH2)3NRCH3ClR=C

32、H3R=HImipramine N-IsopropylmethoxamineNHRCH3OHOCH3OHR=CH(CH3)2 N-isopropylmethoxamineR=H Methoxamine （甲氧明）B. N-Oxidationl Tertiary amines are oxidized to the N-oxides;l whereas secondary and some primary amines are converted into hydroxylamines (羥胺). The formation of hydroxylamines may account for t

33、he toxicity of many aromatic amines.FMO、CYP450 and MAON-Oxidation NCH3CH3RRNCH3CH3ONRNRORNRHRNROHRNH2RNHOHNORRNO2no -hydrogenReversible可逆可逆Tertiary aminesGuanethidine（呱乙啶）NNHHNNH2NNHHNNH2OstableTertiary aminesDapsone（氨苯砜）so2H2NNH2so2H2NNHOH抗麻風(fēng)藥no -hydrogenThe mechanism which some aromatic prime and

34、secondary amines oxide to effect toxicityRNRHRNROHX+RNROXY-OX-RNRYHB:B+HRHNRYX=SO3-, AcAcetaminofluorene(2乙酰氨基芴)NHCOCH3NCOCH3OHNCOCH3OSO3NCOCH3NHCOCH3Nu III. O-Dealkylation of ethersl Oxidative O-dealkylation of ethers is a common metabolic reaction. l The majority of ether groups in drug molecules

35、are aromatic ethers. l These ethers are oxidized by liver microsomal oxidases.The mechanism of O-dealkylationl The mechanism of dealkylation is analogous to that of N-dealkylation, oxidation of the -carbon, and subsequent decomposition of the relatively unstable gem diol. The substituent alkyl group

36、 leaves as a carbonyl derivative.ROCH2RROCHRROCOHR.ROH + RCHOHgem diolCodeine（可待因）CH3NOCH3OOHCH3NOHOOHPhenacetin(非那西汀) C2H5ONHCOCH3HONHCOCH3 acetaminophen 撲熱息痛Indomethacin（吲哚美辛）NCCH3CH2COOHROOClR=CH3R=HInfluencing factors to the rate of O-dealkylationl 1. The rate of O-dealkylation is a function of

37、chain length, i.e., increasing chain length reduces the rate of dealkylation. l 2. Steric factors and ring substituents influence the rate of dealkylation, but are complicated by electronic effects. l 3. Some drug molecules contain more than one ether group, in which case, usually only one ether is

38、dealkylated. Methoxamine （甲氧明）NH2CH3OROCH3OHR=CH3R=HIV. Oxidation of compounds containing sulfurl A. S-Dealkylation l B. Oxidative S-Desulfurationl C. S-Oxidation6-Methylmercaptopurine(6-甲硫嘌呤)NNNHNSCH3NNNHNSCH2OHNNNHNSHA. S-Dealkylation active anticancer drug CYP450B. Oxidative S-DesulfurationC=OP=O

39、P=SC=SThiopental(硫噴妥)HNNHCH3OXHOX = SX = OS-DesulfurationMono-oxygenase殺蟲藥對硫磷O2NPSOC2H5OC2H5O2NPOOC2H5OC2H5磷酸二乙硝苯酯S-DesulfurationMonooxygenaseC. S-OxidationRSRRSORRSO2RFMOor CYP-450Thioridazine(硫利達(dá)嗪)NSNCH3SNSNCH3S CH3OCH3mesoridazine美索達(dá)嗪S-OxidationHigher activity免疫抑制劑OxisuranNCH3SOONCH3SOOOV. Oxidat

40、ion of Alcohols l Alcohol dehydrogenase is an NAD-specific enzyme located in the soluble fraction of tissue homogenates(組織勻漿). l It exhibits a broad specificity for alcohols.RCH2OH + NADRCHO + NADH + H+Metabolisms of AlcoholsMetabolisms of AlcoholsMost primary alcoholsaldehydesother secondarytertiar

41、y alcoholsSome secondary alcoholsconjugationketonesexcretionacidOxidation of ethanolethanoldehydrogenasea microsomal enzyme system (M.E.O.S.)2/3In intoxicationEthylaldehyde1/3Oxidation of Methanol Methanol dehydrogenaseformaldehyde1/6 the rate of ethanolcatalase（過氧化氫酶） xanthine(黃嘌呤）oxidaseEthanol de

42、presses the rate of methanol oxidation by acting as a competitive substrate for alcohol dehydrogenase, reducing the formation of the toxic metabolite. Mefenamic（甲滅酸）COOHNHRCH3R=CH3R=COOHXanthine oxidasealdehyde oxidasedehydrogenase Oxidation of AldehydesEndogenous aldehydesPrimary alcoholsbiogenic a

43、minesexogenous aldehydescarboxylic acids2. Reductionsl I. Carbonyl reduction l II. NO2 reductionl III. Azo reductionI. Reduction of ketonel Ketones are stable to further oxidation and consequently yield reduction products as major metabolites.alcoholsketonesdehydrogenaseAcetohexamide(醋磺己脲)H3CSO2NHCO

44、NHC6H6-cOH3CSO2NHCONHC6H6-cHOHS-(-)A. StereospecificS-(+)-Methadone（美沙酮）CCH2CC2H5OCHCH3N(CH3)2CCH2CC2H5CHCH3N(CH3)2HOHS-()-Methadone3S,6S-(-)-methadolS-(-)StereospecificNaltrexone（納曲酮） NHOOCH2OHONHOOCH2OHOH human 6,-hydroxynaltrexolStereospecificWarfarin（華法林）OOHPhOOR-WarfarinquickB. Stereo-selective

45、II. Nitro Reductionl Nitro compounds are reduced to aromatic primary amines by a nitro-reductase, presumably through nitrosoamine and hydroxylamine intermediates. l These reductases are not solely responsible for the reduction of azo and nitro compounds, probably because of reduction by the bacteria

46、l flora(細(xì)菌群落）in the anaerobic（厭氧）environment of the intestine. The mechanism of nitro reductionRNO2O2O2RNO2RNOH+RNOHe-._.2e-e-.H+RNHOHRNH2e-2e-2H+2H+4-Nitroquinoline-1-oxide(4-硝基喹啉-1-氧化物)NNO2ONNHOHO(carcinogenesis and cell toxicity)Hydroxylamine intermediateNitrobenzene（硝基苯）NO2NHOH正鐵血紅蛋白癥methemoglob

47、inClonazapam（氯硝西泮）NHNOO2NNHNOH2NClClIII. Azo Reduction l A number of azo compounds are converted to aromatic primary amines by CYP-450, NADPH-CYP-450 enzyme system in the liver microsomes and bacterial reductase in the intestine. The mechanism of azo reductionNNArArNNArArNHNHArArO2O2e-._e-_.2e-ArNH2

48、 + ArNH22H+2H+Sulfasalazine(柳氮磺胺吡啶）NNHSO2NNCOOHOHNNHSO2NH2COOHOHH2N+3. Dehalogenation l Oxidative dehydrohalogenation (脫鹵化氫作用)l Reductive dehalogenation (還原脫鹵)l Hydrolytic dehalogenation(水解脫鹵) Oxidative dehydrohalogenationRCH2X RCHOR1R2CHX R1CORRCHX2 RCOXCHX3 XCOX RCOCHX2 RCOCOX H and XCYP-450Chlora

49、mphenicol（氯霉素）CHCHO2NCH2OHOHNHCOCHCl2CHCHO2NCH2OHOHNHCOCCOClCHCHO2NCH2OHOHNHCOCCOproteinproteinOxidative dehydrohalogenationCarbon tetrachloride l CCl4 induces liver necrosis(壞死), which is mediated through an active metabolite. CCl4CCl4-Cl-Cl3CH+O2CHCl3Cl3COO.-.e-:.CCl3CYP450Reductive dehalogenation

50、Halothane 氟烷（1）HCCF3ClBrCHCF3ClHCClCF2FBree_._FClHCCF2_CClCF3HH2CCF3ClRHR.liver toxicityproteinproteinOxidative dehydrohalogenationHalothane 氟烷（2）CHBrClF3CCOHBrClF3CBrCF3COCl_-F3COCproteinCF3COOH + ClproteinH2O4. Hydrolysisl In general, esters and amides are hydrolyzed by enzymes in the blood, liver

51、 microsomes, kidneys, and other tissues. l Esters are rapidly hydrolyzed by esterases (酯酶).The reaction of hydrolysis ROCOR1 ROH+R1COOHRONO2 ROH+HNO3ROSO3H ROH+H2SO4RNHCOR1 RNH2+R1COOHSuccinylcholine（氯化琥珀膽堿）CH2COCH2CH2N+(CH3)3CH2COCH2CH2N+(CH3)3. 2Cl-OOCH2COHCH2COH+ 2 HOCH2CH2N+(CH3)3Cl-OOAspirin（阿司

52、匹林）OCOCH3COOHOHCOOH+ CH3COOHDiphenoxylate（地芬諾酯）CCCH2CH2NCOOC2H5CCCH2CH2NCOOH止瀉作用比原藥強5倍diphenoxylic acid地芬諾酸Atropine（阿托品）l Esters that are sterically hindered are more slowly hydrolyzed and may appear unchanged in the urine. NCH3OCOCC6H5CH2OHOH 50% unchanged 50% unhydrolyzed biotransformed productsAm

53、ides are more stable to hydrolysis than estersl Procainamide（普魯卡因胺）l Procaine（普魯卡因）CONHCH2CH2N(C2H5)2H2NCOOCH2CH2N(C2H5)2H2NPhthalylsulfathiazolesuccinylsulfathiazoleH2NSO2NHSNRCONHSO2NHSNR=HOOCCH2CH2 Phthalylsulfathiazole丁二?；前粪邕騌= succinylsulfathiazole酞磺胺噻唑COOHPhase I may produce one or more of the

54、 following changesl Decreased pharmacologic activity-deactivationl Increased pharmacologic activity-activationl Increased toxicity-intoxicationl Altered pharmacologic activitySection 4 Phase II Biotransformationl The conjugates are more polar and less lipid-soluble than the original drug and, theref

55、ore, will result in more rapid elimination of the drug from tissues. l The conjugation mechanisms are largely responsible for the deactivation and enhanced excretion of many drugs, which would otherwise remain in the body and exert prolonged pharmacologic activity. Classification of Phase IIl 1. Glu

56、curonic acid conjugationl 2. Sulfate conjugationl 3. Conjugation with amino acidsl 4. Glutathione conjugation l 5. Acetylationl 6. MethylationP-aminosalicylicNH2OHCOOHAcetylationO-Sulfate conjugationN-Glucuronic acid conjugationO-Glucuronic acid conjugationGlucuronic acid conjugationConjugation with

57、 glycineActivated intermediates in Phase II reactionl As a rule, the conjugating intermediate does not react directly with the drug, but either in an activated form or with an activated form of the drug. l Most often these activated intermediates are nucleotides(核苷酸), and the reaction is catalyzed b

58、y specific transferases(轉(zhuǎn)移酶).1. Glucuronic Acid Conjugationl Glucuronide (葡萄糖醛酸) formation is one of the most common routes of drug metabolism and accounts for a major share of the metabolites. l Its significance lies in the readily available supply of glucuronic acid in liver and in the large numbe

59、r of functional groups forming glucuronide conjugates. l Invariably, the glucuronide conjugates are pharmacologically inactive.l The reaction involves the condensation of the drug or its biotransformation product with the activated form of glucuronic acid, uridine diphosphate glucuronic acid (尿苷-5-二

60、磷酸-D-葡糖醛酸,UDPGA).Uridine Diphosphate Glucuronic Acid (UDPGA)Glucuronic Acid ConjugationlX=-O-、-N-、-S-、-OCO-。HXRglucuronyl transferase (UDP-葡醛酸轉(zhuǎn)移酶)water solubilityThe action of glucuronidationl With the attachment of the hydrophilic carbohydrate moiety containing an ionizable carboxyl group, a lipid-