The cis-and trans-structures assigned to nerol and geraniol respectively have been confirmed. biosynthesis of squalene, has been rigorously established. asymmetric centres.The trans. trans-structure of the common form of farnesol, and of the farnesyl pyrophosphate invotved in the Phytol has been shown to have a trans-configuration about the double bond, and an R-configuration a t both i A ~ the commencement of these studies little information was available concerning the stereochemistry of the acyclic terpenes containing primary allylic systems.Geraniol (Va) was believed to have the tram-configuration * because it cyclises in acids to a-terpineol more slowly than its geometrical isomer, nerol.2 Farnesol * With trisubstituted double bonds, the terms cis and trans are used to designate the relative positions of the two largest substituents.

The gas chromatography‐mass spectrometry (GC‐MS) method developed in the preceding papers was extended to the analysis of autoxidation products of methyl linolenate. Four isomeric hydroxy allylic trienes with a conjugated diene system were identified after reduction of the linolenate hydroperoxides. All eight geometrictrans,cis‐ andtrans, trans‐conjugated diene isomers of these hydroxy allylic compounds were identified and partially separated by GC of the trimethylsilyl (TMS) ether derivatives. The proportion found of 9‐ and 16‐hydroperoxides was significantly higher (75–81%) than the 12‐ and 13‐hydroperoxides (18–25%). The tendency of the 12‐ and 13‐hydroperoxides to form cyclic peroxides, cyclic peroxidehydroperoxides, and prostaglandin‐like endoperoxides was supported by indirect evidence for the presence of 9,10,12‐ and 13,15,16‐trihydroxyoctadecanoate in hydrogenated derivatives of the highly oxygenated products. The quantitative GC‐MS method was used to determine the relative contribution of linolenate, linoleate, and oleate in mixtures to the formation of hydroperoxides.

Methods have been developed, using ' 3C n.m.r. spectroscopy and mass spectrometry, for the analysis of all eight cis and trans allylic 8-, 9 -, lo-, and 1 1 -hydroperoxides formed on autoxidation of methyl oleate.The autoxidation of fatty acids, and their derivatives, has received much attention recently because lipid hydroperoxides have been shown to be precursors of prostaglandin-related endoperoxides,2 and to play a role in photocarcinogenesis, in the destruction of proteins and bi~membranes,~ and in chemically induced t ~x i c i t y . ~ Although the autoxidation of methyl oleate (1) and related compounds has been the subject of many investigations (see for example 6-8), the stereochemical course of this reaction had not been fully established prior to the studies now reported (for preliminary publication see ref. 9).In view of the instability of the allylic hydroperoxides (3)-(6) formed on autoxidation of methyl oleate, attention was first directed to devising methods for the analysis of the mixtures of allylic alcohols (7)-(10) readily obtained by borohydride reduction of the initial autoxidation products (evidence is given later that these reductions involve no loss in stereochemistry). To develop suitable procedures for analysing such mixtures, four authentic hydroxyoctadecenoates, cis-and trans-(1 1) and (8), were prepared by unambiguous methods.The trans-isomer of (1 1) was conveniently obtained from ricinoleic acid (12), via the keto-ester (13), by known procedures (see Experimental section). Reaction of the silver salt of the readily available methyl undec-10-ynoate '**' * with heptanoyl chloride gave the expected acetylenic ketone (14). Reduction of Me[CH,],CH=CH[CH,],CO,Me(1) cis-9 (2) Irans-9 Me[CH,],CH=CHCH(OOH)[CH,],CO,Me(3) x = 6, y = 7 (4) x = 7, y = 6 Me[CH,],CH(OOH)CH=CH[CH,],CO,Me(5) x = 6, y = 7 ( 6 ) x = 7, . Y = 6 Me[CH2],CH=CHCH(OH)[CH2],CO2Me (7) x = 6, y = 7 (8) x = 7, = 6 (9) x = 6, J.' = 7 (10) x = 7, 4' = 6 (11) x = 8, y = 5

The gas chromatography-mass spectrometry (GC-MS) approach developed in the preceding paper was applied for qualitative and quantitative investigations of autoxidation products of methyl linoleate. A GC-MS computer summation method was standardized with synthetic 9- and 13-hydroxyoctadecanoate. Equal amounts of 9- and 13-hydroperoxides were found in all samples of linoleate autoxidized at different temperatures and peroxide levels. The results are consistent with the classical free radical mechanism of autoxidation involving a pentadiene intermediate having equivalent sites for oxygen attack at carbon-9 and carbon-13. Minor oxygenated products of autoxidation indicated by GC-MS include keto dienes, epoxyhydroxymonoenes, di- and tri-hydroxy monoenes. These hydroxy compounds are presumed to be present in the form of hydroperoxides. The quantitative GC-MS method was found suitable for the analysis of autoxidized mixtures of oleate and linoleate. By this method, it is possible to determine the origin of the hydroperoxides formed in mixtures of these fatty esters.

A structural investigation of autoxidation products of methyl oleate was carried out by gas chromatography-mass spectrometry (GC-MS) of trimethylsilyl (TMS) ether derivatives. GC-MS using computer plots of selected masses afforded structural assignments of GC peaks due to incompletely resolved mixtures. This method provided evidence of epoxy and keto esters which are not completely separated from the main components consisting of the TMS derivatives of the allylic hydroxy esters. Use of an MS-computer system also showed that the hydroxyoctadecanoate TMS ethers were partially separated by GC. The use of synthetic hydroxyoctadecanoates for the first time enabled us to demonstrate the quantitative reliability of a GC-MS computer summation approach to analyze the isomeric composition of oleate hydroperoxides (as the saturated TMS ether derivatives). Consistently higher concentrations were found of the 8- and 11-hydroperoxides than of the 9- and 10-hydroperoxides. Minor products of autoxidation identified by GC-MS include allylic enones, isomeric epoxyoctadecanoates, dihydroxyoctadecenoates, and dihydroxyoctadecanoates.