No abstract

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 0.r.d. curves of ca. 40 carotenoids have been measured, chiefly in dioxan, over the range 400-200 nm. The chromophore in all cases is a conjugated polyene system which is perturbed by one or two chiral end-groups.The curves are analysed in terms of the simple additivity of the effects of end-groups, and the absolute configurations of several compounds have been provisionally assigned.MANY carotenoids contain one or more asymmetric carbon atoms, but little information is available concerning the absolute or relative configurations of these centres. Capsanthin (1) has been degraded to the acid (2) which on further oxidation, gave (-)-camphoronic acid (3),2 also obtained from (+)-camphor (4) of known 3 absolute configuration. Since the two oxygen functions This paper is Part LXII in the Westfield College series on optical rotatory dispersion, preceding paper, Part LXI, G.

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