7- Methyloctanoic acid

Two related scarab species produce ethyl 4-methyloctanoate 78 (Scheme 8) as an aggregation pheromone the African rhinoceros beetle Oryctes monoceros [170] and the coconut rhinoceros beetle Oryctes rhinoceros [171, 172]. The latter is readily attracted to the racemate. Its secretion was found to contain the free acid as well as ethyl 4-methylheptanoate [ 171 ]. Similarly to other cases, the attractiveness of ethyl 4-methyloctanoate is enhanced by host compounds, i.e. coconut wood [173]. The date palm fruit stalk borer, Oryctes elegans, uses 4-methyloctanoic acid as a male produced pheromone [174]. Structurally... 

An extract of secretion from the sebaceous glands on head and neck of sexually active feral billygoats increases the number of does ovulating. The extract was placed on cotton wool and worn in facemasks. 4-Ethyloctanoic acid and 4-methyloctanoic acid, responsible for the goaty odor, were not active but both the free fatty acid and lipid-free non-acid fractions were. The 4-ethyl branched fatty acids are present in the active fraction (Birch etal., 1989). 

Kinetic resolution of branched-chain fatty acids has been reported recently by Franssen et al. [24]. With the help of immobilised Candida antarctica lipase B, racemic 4-methyloctanoic acid (responsible for sheep-like and goat-like flavours in sheep and goat milk and cheese, respectively) was esterified with ethanol. Only the R ester could be obtained, whereas (S)-4-methyloctanoic acid was not converted (Scheme 22.1). 

Scheme 22.1 Kinetic resolution of racemic 4-methyloctanoic acid with Candida antarctica lipase B[24]...

Esters formed during heating of lipids are contributors to pork flavor. Raw pork contains only a small number of esters, while cooked pork contains significantly more, and acetates are the most prominent volatiles. Esters of cooked pork are derived from C1-Ci0 acids, which impart a fruity sweet note to pork meat (J16). Beef contains a higher proportion of esters derived from long chain fatty acids which possess a more fatty flavor character (16). The characteristic odor of mutton is believed to be due to the evolution of 4-methyloctanoic acid, 4-methylnonanoic acid and similar compounds during heating (17). 

Esters of fatty alcohols and 4-methyloctanoic acid (the acid part of Ml — possibly derived from a sequence involving acetate—acetate—propanoate—acetate) are components of the Dufour gland secretion of the ant Gnamptogenys moelleri 866... 

Some esters of long-chain saturated fatty acids are aggregation pheromone beetles. The ethanol-ester of 4-methyloctanoic acid is, for instance, a commercialized aggregation pheromone (Oryctalure ) used to control the coconut rhinoceros beetle (Oryctes rhinoceros) (Morin et al., 1996). American palm weevil (Rhynchphorus palmarum) is attracted by the aggregation pheromone 6-methyl-2-hepten-4-ol. The pheromone has been tried for control of the weevil and is sold under the names Rhyncopherol and Rhynkolure . 

In comparison, the ester hydrolysis of ibuprofen (2 -chloroethyl)ester catalyzed by the same enzyme proceeded with an E value of only 3.5 [2f The same phenomenon has been observed in the ammoniolysis of 4-methyloctanoic acid. Here an E value of 76 was determined for ammoniolysis, whereas in the transesterification reaction an E-value of only 23 was found15, 6). 

For example, lamb/mutton has a distinctive aroma, which to some extent determines its lesser popularity. The main aromatic component of heat-treated meat is an unusual, branched fatty acid 4-ethyloctanoic acid (8-183) that has a waxy, fatty, creamy, moldy, sour sweaty, cheesy odour with animal-like nuances, and occurs as an almost racemic mixture of the enantiomers. The odour thresholds of the +)- R)- and (-)-(S)-enantiomers are <13 and <6 xg/l in air, respectively. 4-Ethyloctanoic acid (also identified in stewed beef gravy and goat and sheep cheeses) is accompanied by 4-methyloctanoic acid. The 4-ethyloctanoic acid content is approximately the same in raw meat but higher in fat. 

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