《有机化学》课程教学资源（教材文献，英文版）CHAPTER 26 LIPIDS

CHAPTER 26 LIPIDS SOLUTIONS TO TEXT PROBLEMS 26.1 The triacylglycerol shown in text Figure 26.2a, with an oleyl group at C-2 of the glycerol unit and two stearyl groups at C-I and C-3, yields stearic and oleic acids in a 2: I molar ratio on hydrolysis. A constitutionally isomeric structure in which the oleyl group is attached to C-l of glycerol would yield the same hydrolysis products. O CH,OC(CH2)16CH3 O CH,OC(CH,),CH-CH(CH,),CH3 CH3(CH,)7CH=CH(CH2),COCH CH3(CH,)16COCH CH,OC(CH,)16CH3 CH,OC(CH,),CH CH3(CH2)CH=CH(CH2),COH HOCH 2HOC(CH2)1CH CHO Oleic acid Stearic acid 731 Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website

731 CHAPTER 26 LIPIDS SOLUTIONS TO TEXT PROBLEMS 26.1 The triacylglycerol shown in text Figure 26.2a, with an oleyl group at C-2 of the glycerol unit and two stearyl groups at C-1 and C-3, yields stearic and oleic acids in a 2 : 1 molar ratio on hydrolysis. A constitutionally isomeric structure in which the oleyl group is attached to C-1 of glycerol would yield the same hydrolysis products. CH or 3(CH2)7CH CH(CH2)7COCH CH2OC(CH2)16CH3 CH2OC(CH2)16CH3 O O O CH3(CH2)16COCH O CH2OC(CH2)7CH CH(CH2)7CH3 CH2OC(CH2)16CH3 O O 3H2O CH3(CH2)7CH CH(CH2)7COH O Oleic acid HOCH CH2OH CH2OH Glycerol 2HOC(CH2)16CH3 O Stearic acid Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

732 LIPIDS 26.2 The sulfur of acyl carrier protein acts as a nucleophile and attacks the acetyl group of acetyl coenzyme A CH CSCoA HS-ACP CHC-SCOA CH2CS一ACP+ HSCOA S--ACP Acyl carrier coenzyme A 26.3 Conversion of acyl carrier protein-bound tetradecanoate to hexadecanoate proceeds through the series of intermediates shown CH3(CH)12CS--ACP HO CCH.CS-ACP CHa(CH2)12CCHaCS--ACP CH3(CH)12CHCHCS-ACE CHa(CH,)12CH=CHCS--ACP CH,(CH,)12CH, CH,CS--ACP 26.4 The structure of L-glycerol 3-phosphate is shown in a Fischer projection. Translate the Fischer pro- jection to a three-dimensional representation CH,OH HO. CHIOH HO saine as C-H CH,OPO3H2 CH,OPO,H2 H,O POCH Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website

732 LIPIDS 26.2 The sulfur of acyl carrier protein acts as a nucleophile and attacks the acetyl group of acetyl coenzyme A. 26.3 Conversion of acyl carrier protein–bound tetradecanoate to hexadecanoate proceeds through the series of intermediates shown. 26.4 The structure of L-glycerol 3-phosphate is shown in a Fischer projection. Translate the Fischer pro￾jection to a three-dimensional representation. CH2OH HO H CH2OPO3H2 HO C H same as H CH2OH CH2OPO3H2 C HO CH2OH H2O3POCH2 O CH3(CH2)12CS ACP O O CH3(CH2)12CCH2CS ACP OH O CH3(CH2)12CHCH2CS ACP O HO2CCH2CS ACP O CH3(CH2)12CH2CH2CS ACP O CH3(CH2)12CH ACP CHCS CH3CSCoA HSCoA HS CH3C CH3CS ACP ACP O O SCoA ACP S O H Acetyl coenzyme A Acyl carrier protein Tetrahedral intermediate S-Acetyl acyl carrier protein Coenzyme A Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

LIPIDS 733 The order of decreasing sequence rule precedence is Ho->H,O, POCH,>HOCH2->H When the three-dimensional formula is viewed from a perspective in which the lowest ranked sub- stituent is away from us, we see HOCH, OH iguration is r so. The conversion of L-glycerol 3-phosphate to a phosphatidic acid does not affect any of the bonds the stereogenic center, nor does it alter the sequence rule ranking of the substituents RCO CH,OCR H H,O, POCH 26.5 Cetyl palmitate(hexadecyl hexadecanoate)is an ester in which both the acyl group and the alkyl group contain 16 carbon atoms CH;(CH,)1CO(CH)15CH3 26.6 The structure of PGE is found in text Figure 26.5 COOH CH The problem states that PGe, has one more double bond than PGe and that it is biosynthe from arachidonic acid. Arachidonic acid (text Table 26. 1) has a double bond at C-5, and thus COOH several steps Arachidonic acid Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website

The order of decreasing sequence rule precedence is When the three-dimensional formula is viewed from a perspective in which the lowest ranked sub￾stituent is away from us, we see The absolute configuration is R. The conversion of L-glycerol 3-phosphate to a phosphatidic acid does not affect any of the bonds to the stereogenic center, nor does it alter the sequence rule ranking of the substituents. The absolute configuration is R. 26.5 Cetyl palmitate (hexadecyl hexadecanoate) is an ester in which both the acyl group and the alkyl group contain 16 carbon atoms. 26.6 The structure of PGE1 is found in text Figure 26.5. The problem states that PGE2 has one more double bond than PGE1 and that it is biosynthesized from arachidonic acid. Arachidonic acid (text Table 26.1) has a double bond at C-5, and thus PGE2 has the structure shown. several steps Arachidonic acid 5 CH3 COOH PGE2 OH CH3 COOH HO O 5 HO O COOH OH CH3 PGE1 CH3(CH2)14CO(CH2)15CH3 O Hexadecyl hexadecanoate C CH2OCR H RCO H2O3POCH2 H2O3POCH2 O RCO O O   RCOCH2  O H HOCH2 OH C H2O3POCH2 Order of decreasing rank is clockwise, therefore R. HO H  H2O3POCH2  HOCH2  LIPIDS 733 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

734 LIPIDS 26.7 Isoprene units are fragments in the carbon skeleton. Functional groups and multiple bond tre ignored when structures are examined for the presence of isoprene units. ax-Phellandrene(two equally correct answers) Menthol(same carbon skeleton as ae-phellandrene but different functionality) Citral ae-Selinene is shown in text Section 26.7 Farnesol OH Abscisic acid TOH Co2 embrene(two equally correct answers ): Vitamin a Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website

26.7 Isoprene units are fragments in the carbon skeleton. Functional groups and multiple bonds are ignored when structures are examined for the presence of isoprene units. -Phellandrene (two equally correct answers): Menthol (same carbon skeleton as -phellandrene but different functionality): Citral: -Selinene is shown in text Section 26.7. Farnesol: Abscisic acid: Cembrene (two equally correct answers): Vitamin A: OH or OH CO2H O OH CH O or OH OH or 734 LIPIDS Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

LIPIDS 735 26.8 B-Carotene is a tetraterpene because it has 40 carbon atoms. The tail-to-tail linkage is at the midpoint of the molecule and connects two 20-carbon fragments 人 Tail-to-tail link between isoprene units 26.9 Isopentenyl pyrophosphate acts as an alkylating agent toward farnesyl pyrophosphate Alkylation is followed by loss of a proton from the carbocation intermediate, giving geranylgeranyl pyrophos phate. Hydrolysis of the pyrophosphate yields geranylgeraniol Farnesyl pyrophosphate sopentenyl pyrophosphate OPP OPP Geranylgeranyl pyrophosphate Geranylgeraniol 26.10 Borneol, the structure of which is given in text Figure 26.7, is a secondary alcohol. Oxidation of borneol converts it to the ketone H. CrC Borneol Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website

26.8 -Carotene is a tetraterpene because it has 40 carbon atoms. The tail-to-tail linkage is at the midpoint of the molecule and connects two 20-carbon fragments. 26.9 Isopentenyl pyrophosphate acts as an alkylating agent toward farnesyl pyrophosphate. Alkylation is followed by loss of a proton from the carbocation intermediate, giving geranylgeranyl pyrophos￾phate. Hydrolysis of the pyrophosphate yields geranylgeraniol. 26.10 Borneol, the structure of which is given in text Figure 26.7, is a secondary alcohol. Oxidation of borneol converts it to the ketone camphor. OH H H2CrO4 O Borneol Camphor OPP H H Geranylgeranyl pyrophosphate OPP Geranylgeraniol OH H H2O Farnesyl pyrophosphate OPP Isopentenyl pyrophosphate OPP Tail-to-tail link between isoprene units LIPIDS 735 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

736 LIPIDS Reduction of camphor with sodium borohydride gives a mixture of stereoisomeric alcohols, of which one is borneol and the other isoborneol oH Borneol Isoborneol 26.11 Figure 26.8 in the text describes the distribution ofC(denoted by *)in citronellal biosynthesized from acetate enriched withC in its methyl group CH.H CH If, instead, acetate enriched with C at its carbonyl carbon were used, exactly the opposite distribu- tion of the C label would be observed CH- COH WhenCH, CO, H is used, C-2, C-4, C-6, C-8, and both methyl groups of citronellal are labeled. When CH3CO, H is used, C-1, C-3, C-5, and C-7 26.12 (b) The hydrogens that migrate in step 3 are those at C-13 and c-17(steroid numbering) As shown in the coiled form of squalene 2, 3-epoxide, these correspond to hydrogens at C-14 and C-18(systematic IUPAC numbering) (c) The carbon atoms that form the C, D ring junction in cholesterol are C-14 and c-15 of squalene 2,3-epoxide. It is the methyl group at C-15 of squalene 2, 3-epoxide that becomes the methyl group at this junction in cholesterol Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website

736 LIPIDS Reduction of camphor with sodium borohydride gives a mixture of stereoisomeric alcohols, of which one is borneol and the other isoborneol. 26.11 Figure 26.8 in the text describes the distribution of 14C (denoted by *) in citronellal biosynthesized from acetate enriched with 14C in its methyl group. If, instead, acetate enriched with 14C at its carbonyl carbon were used, exactly the opposite distribu￾tion of the 14C label would be observed. When 14CH3CO2H is used, C-2, C-4, C-6, C-8, and both methyl groups of citronellal are labeled. When CH3 14CO2H is used, C-1, C-3, C-5, and C-7 are labeled. 26.12 (b) The hydrogens that migrate in step 3 are those at C-13 and C-17 (steroid numbering). As shown in the coiled form of squalene 2,3-epoxide, these correspond to hydrogens at C-14 and C-18 (systematic IUPAC numbering). (c) The carbon atoms that form the C, D ring junction in cholesterol are C-14 and C-15 of squalene 2,3-epoxide. It is the methyl group at C-15 of squalene 2,3-epoxide that becomes the methyl group at this junction in cholesterol. HO H CH3 O H H H 14 15 18 HO H H 13 17 * * * * CH O * CH3CO2H CH3CO2H * CH * * O * * * * NaBH4 O OH H Borneol H OH Camphor Isoborneol Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

LIPIDS 737 (d) The methyl groups that are lost are the methyl substituents at C-2 and C-10 plus the methyl group that is C-1 of squalene 2, 3-epoxide O 26.13 Tracking theC label ofCH,CO, H through the complete biosynthesis of cholesterol requires a systematic approach. First, by analogy with Problem 26.11, we can determine the distribution of C (denoted by *)in squalene 2.3-epoxid Next, follow the path of the C-enriched carbons in the cyclization of squalene 2, 3-epoxide to Lanosterol Cholesterol Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website

(d) The methyl groups that are lost are the methyl substituents at C-2 and C-10 plus the methyl group that is C-1 of squalene 2,3-epoxide. 26.13 Tracking the 14C label of 14CH3CO2H through the complete biosynthesis of cholesterol requires a systematic approach. First, by analogy with Problem 26.11, we can determine the distribution of 14C (denoted by *) in squalene 2,3-epoxide. Next, follow the path of the 14C-enriched carbons in the cyclization of squalene 2,3-epoxide to lanosterol. *** ***** * * * * * * * * * * O then on to cholesterol * * * * * * * * * * * * * * * * HO * * * * Lanosterol * * * * * * * * * * * * * * HO * * Cholesterol * * * * * * * * HO * * * * * * * *** * * * * * * * * * ****** O O H 2 10 CH3 CH3 CH3 LIPIDS 737 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

738 LIPIDS 26.14 By analogy to the reaction in which 7-dehydrocholesterol is converted to vitamin D3, the structure of vitamin D, can be deduced from that of ergosterol. HOˇ HO Vitamin d Vitamin d 26.15 (a) Fatty acid biosynthesis proceeds by the joining of acetate units. oO CH3CSCoA CH,CCH,CSCoA CH3(CH,)CSCoA Acetyl coenzyme A Acetoacetyl coenzyme A Palmitoyl Thus. the even-numbered carbons will be labeled with C when acid is biosynthe sized from CH COH CH CH,CH, CH, CH,CH, CH, CH,CH, CH, CH,CH2CH,CH, CH,CO,H (b) As noted in Problem 26.6, arachidonic acid (Table 26. 1)is the biosynthetic precursor of Pge. The distribution of the C label in PGE, biosynthesized from CH, CO, H reflects the fatty acid origin of the prostaglandins COOH (c) Limonene is a monoterpene, biosynthesized from acetate by way of mevalonate and isopen tenyl pyrophosphate CH COH OPP Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website

26.14 By analogy to the reaction in which 7-dehydrocholesterol is converted to vitamin D3, the structure of vitamin D2 can be deduced from that of ergosterol. 26.15 (a) Fatty acid biosynthesis proceeds by the joining of acetate units. Thus, the even-numbered carbons will be labeled with 14C when palmitic acid is biosynthe￾sized from 14CH3CO2H. (b) As noted in Problem 26.6, arachidonic acid (Table 26.1) is the biosynthetic precursor of PGE2. The distribution of the 14C label in PGE2 biosynthesized from 14CH3CO2H reflects the fatty acid origin of the prostaglandins. (c) Limonene is a monoterpene, biosynthesized from acetate by way of mevalonate and isopen￾tenyl pyrophosphate. 14CH3CO2H Acetic acid Isopentenyl pyrophosphate OPP * * * Limonene * * * * * * * * * * * * * * * * PGE2 OH CH3 COOH HO O CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CO2H ******** CH3CSCoA O CH3CCH2CSCoA O CH3(CH2)14CSCoA O O Acetyl coenzyme A Acetoacetyl coenzyme A Palmitoyl coenzyme A light 7-Dehydrocholesterol Vitamin D3 HO H H HO H light Ergosterol Vitamin D2 HO H H HO H 738 LIPIDS Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

LIPIDS 739 (d) The distribution of theC label in B-carotene becomes evident once its isoprene units are 26.16 The carbon chain of prostacyclin is derived from acetate by way of a Czo fatty acid. Trace a contin- uous chain of 20 carbons beginning with the carboxyl group. Even-numbered carbons are labeled withC when prostacyclin is biosynthesized fromCH, CO,H COOH HO 26.17 The isoprene units in the designated compounds are shown by disconnections in the structural (a) Ascaridole (b) Dendrolasin (c) bisabolene (d) a-Santonin Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website

(d) The distribution of the 14C label in -carotene becomes evident once its isoprene units are identified. 26.16 The carbon chain of prostacyclin is derived from acetate by way of a C20 fatty acid. Trace a contin￾uous chain of 20 carbons beginning with the carboxyl group. Even-numbered carbons are labeled with 14C when prostacyclin is biosynthesized from 14CH3CO2H. 26.17 The isoprene units in the designated compounds are shown by disconnections in the structural formulas. (a) Ascaridole: (b) Dendrolasin: (c) -Bisabolene (d) -Santonin CH3 CH3 O O CH3 O or O or O O O O Prostacyclin HO OH COOH CH3 O *** * * * * * * * -Carotene * * * * * * * **** * * * * * * * * * * * * * LIPIDS 739 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

740 LIPIDS e) Tetrahymanol Tail-to-tail linkage of isoprene units CH CH H C CH 26.18 Of the four isoprene units of cubitene, three of them are joined in the usual head-to-tail fashion, but the fourth one is joined in an irregular way Irregular linkage of this isoprene unit to remainder of molecule 26.19(a) Cinerin I is an ester, the acyl portion of which is composed of two isoprene units, as follows b) Hydrolysis of cinerin I involves cleavage of the ester unit. H HO (+)-Chrysanthemic Chrysanthemic acid has the constitution shown in the equation. Its stereochemistry is revealed COH 2.oxidatio COH Ch CCH Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website

(e) Tetrahymanol 26.18 Of the four isoprene units of cubitene, three of them are joined in the usual head-to-tail fashion, but the fourth one is joined in an irregular way. 26.19 (a) Cinerin I is an ester, the acyl portion of which is composed of two isoprene units, as follows: (b) Hydrolysis of cinerin I involves cleavage of the ester unit. Chrysanthemic acid has the constitution shown in the equation. Its stereochemistry is revealed by subsequent experiments. 1. O3 2. oxidation O O COH ()-Chrysanthemic acid O O COH HOC ()-Caronic acid CH3CCH3 Acetone H2O O O Cinerin I O COH ()-Chrysanthemic acid HO O O O O O Cinerin I Irregular linkage of this isoprene unit to remainder of molecule H3C CH3 CH3 CH3 CH3 CH3 OH H3C CH3 Tail-to-tail linkage of isoprene units 740 LIPIDS Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website