2- Methyl-5-hydroxyhexanoic acid lactone

Wheeler et al. (1976) showed that the secretions of Xylocopa hirsutissima (Xylocopinae) are dominated by c/5-2-methyl-5-hydroxyhexanoic acid lactone. In addition, traces of benzaldehyde, />-cresol, benzoic acid, and vanillin were detected. 

All four possible diastereomers of 2-methyl-5-hydroxyhexanoic acid lactone (628) have been synthesized by Pirkle and Adams (641) and await comparison with natural material to determine which is the pheromone of the carpenter bee. 

Tertiary alcohols are oxidized in water-dioxane-NaOH to alkoxy radicals, wliich fragmentate to ketone and alkyl radicals R- (Eq. (216) ). The relative rate of cleavage decreases with R in the order sec -butyl > isopropyl > ethyl > propyl > pentyl > isobutyl > methyl 46 8). Likewise, the bisulfite adduct of cyclohexanone is converted in 20% yield to 4-hydroxyhexanoic acid lactone (160) and 3-hydroxycyclohexanoic acid lactone (161) by anodic fragmentation (Eq. (222) ) 469 ... 

In addition, n-hexanoic acid, methyl (X)-7-hexadecenoate and 4-hydroxyhexanoic acid lactone (T-caprolactone) (XV) have been identified as part of the sex attractant blend. All of these compounds are individually active. 

Synonyms 5-Caprolactone 5-Hexanolactone 5-Hexanolide 5-Hydroxyhexanoic acid lactone 5-Methyl-5-valerolactone Tetrahydro-6-methyl-2H-pyran-2-one... 

Males of the carpenter bee, Xylocopa hirutissima, establish and defend territories that are located proximate to projecting trees on mountain tops (146). These territories are maintained by a mandibular gland secretion that contains, as a major constituent, the cis-lactone of 2-methyl-5-hydroxyhexanoic acid (XXXVIII) (147). 

Figure VIII shows the enantiomeric composition of various hydroxy- and acetoxyacid esters and of if -hexa-and -octalactone isolated from pineapple. Methyl 3-hydroxyhexanoate and methyl 3-acetoxyhexanoate are mainly of the (S)-configuration corresponding to intermediates of B-oxidation. The optical purity of the 5-acetoxy esters is lower than of the 3-acetoxy derivatives. The lactones were mainly of the (R)-configuration. Figure IX presents a possible pathway to explain the formation of these compounds. Methyl (S)-(+)-3-hydroxyhexanoate and methyl (S)-3-acetoxyhexanoate may be derived from (S)-3-hydroxyhexanoyl-CoA by transacylation with methanol and acetyl-CoA, respectively. The biosynthesis of 5-hydroxyacids is still unknown, but they may be formed by elongation of 3-hydroxyacids with malonyl-ACP. This hypothesis could explain their varying enantiomeric composition relative to the 3-hydroxyacids. However, hydration of unsaturated acids and/or the reduction of 5-oxoacids may be involved.

Esters constituted the largest family and included acetates (ethyl, propyl, isobutyl, butyl, isoamyl, and phenethyl), ethyl esters of fatty acids (propanoate, isobutanoate, butanoate, hexanoate, octanoate, 3-hydroxybutanoate, 3-hydroxyhexanoate and furcate), ethyl esters of organic acids (pyruvate, lactate, ethyl myristate, diethyl malate and, mono- and diethyl succinate) and various other esters, such as methyl butanoate, isobutyl lactate and phenylethyl octanoate. The acids quantified included isobutanoic, butanoic, hexanoic, octanoic, decanoic, lauiic and 3-methylbutanoic. The lactones included y-butyrolactone, pantolactone, y-decalactone and E- and Z-oak lactone and the terpenes included neral d-terpineol, P-dtronellol and Z-nerolidol. The aldehyde family comprised acetaldehyde, benzaldehyde, furfural, 5-methylfurfural and octanal, and the phenol family included eugenol, 4-ethylphenol and 4-ethylguaiacol. Finally, 1,1-diethoxyethane, acetoin, sotolon, 2, 3-butanedione, p-cymene and methionol were also determined. 

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