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 projection 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 substituent 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 pyrophosphate. 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