3- Methyl- -2-hexenoic acid

Methyl-2-hexenoic acid (mixture of ll and Z isomers) has been identified as the substance responsible for the odor of human sweat. Synthesize the compound from starting materials having five or fewer carbons. 

Humans Homo sapiens (E)-3-Methyl-2-hexenoic acid Axilla Zeng etal., 1991... 

Axillary odors of male and female humans contain the same compounds (Ce-Cii acids andE-3-methyl-2-hexenoic acid), but in different ratios. The characteristic odor resides in acidic compounds (Zeng etal, 1996b). 

Besides steroids, axillary odor also contains normal, branched, unsaturated aliphatic acids with 6 to 11 carbon members. Most abundant is (E)-3-methyl-2-hexenoic acid. Both this compound and its (Z)-isomer are found in the aqueous phase hydrolysate and the aqueous phase incubated with bacteria. It is assumed that precursors are water soluble and converted to odoriferous compounds by the axillary flora (Zeng etal., 1992). 

The compound responsible for much of the underarm odor is 3-methyl-2-hexenoic acid in both its (E) and (Z) isomers (Zeng et ah, 1991). Breath can also communicate gender information. However as with axillary odor, breath from men tends to be classified as stronger and more unpleasant than that of women Doty etal, 1982). 

Sweat acid 3-Methyl-2-hexenoic acid CH3CH2CH2C(CH3)=CHC02H Armpits... 

Rabinowitz, J.L., and Zanger, M., The synthesis of " C-tran -3-methyl-2-hexenoic acid labeled in various positions, 7. Labelled Compd., 8, 657, 1972. 

G.13) 2(5/f)-Furanone, 5-ethyl-3-hydroxy-4-methyl-, 2-hydroxy-3-methylhex-2-eno-4-lactone, 5-ethyl-2,5-dihydro-3-hydroxy-4-methylfuran-2-one, 4-ethyl-2-hydroxy-3-methyl-2-buten-4-olide, 2,4-dihydroxy-3-methyl-2-hexenoic acid, 7-lactone, a-hydroxy-p-methyl-Aa,p-7-hexenolactone, abhexone 698-10-2] FEMA 3153 ( )- 1144810-13-9] (/ )- 144831-60-7J (5)- 14483l-61-8]... 

Pierce, Jr., J. D., Blank, D. H., Aronov, E. V., Guo, Z., Preti, G., and Wysocki, C. J., 1996, Cross-adaptation of sweaty-smelling 3-methyl-2-hexenoic acid by its ethyl esters is determined by structural similarity, J. Soc. Cosmet. Chem. 47 363-75. 

The first members of the carboxylic acid series are colorless liquids with sharp or unpleasant odors. Acetic acid, which constitutes about 4% to 5% of vinegar, provides the characteristic odor and flavor. Butyric acid gives rancid butter its disagreeable odor, and the goat acids (caproic, caprylic, and capric in Table 10.1) smell like goats. 3-Methyl-2-hexenoic acid, produced by bacteria, is responsible for the offensive odor of human armpits. Table 10.3 lists some physical properties of selected carboxylic acids. 

Several alkyl-branched fatty acids were found to be powerful and characteristic food flavors. 2-Methylbutyric acid is an important constituent of the aroma of cranberry Vaccinium vitis-idaea L.) (77). 3-Methyl-valeric acid and isovaleric acid were identified in tobacco leaves and found to contribute to the distinct sensory properties of Turkish tobacco smoke 590). Isovaleric acid, which has the lowest flavor threshold (0.7 ppm) 522) of all saturated fatty acids, is regarded as an essential flavor component of Limburger cheese (575). ( )-3-Methyl-2-hexenoic acid was recognized as the malodorous component of schizophrenics sweat (579). The undesirable odor of mutton can be attributed to branched-chain and unsaturated fatty acids having 8 to 10 carbon atoms. The 4-methyl-branched acids and in particular 4-methyloctanoic and 4-methyl-... 

This is ( )-3-methyl-2-hexenoic acid (a.k.a. ran5-3-methyl-2-hexenoic acid). It is one of 30 or more smelly molecules in body odor, but this is reckoned to be simply the best . 

Chapter 56 Sweaty Acid, ( )-3-Methyl-2-Hexenoic Acid ... 

Natsch, A., H. Gfeller, RGygax, J. Schmid and G. Acuna,/. Biol. Chem., 278, 2003, 5718-5727. (Enzyme release of 3-methyl-2-hexenoic acid and 3-hydroxy-3-methylhexanoic acid.)... 

The actual compositions of malodors are invariably even more complex than those just quoted and one which has received considerable attention is sweat-generated body malodor. Quite remarkably, it was only as recently as 1990 that Dr. George Preti of Monell reported at an American Chemical Society meeting that 3-methyl-2-hexenoic acid is the chief cause of underarm odor. It had previously been widely assumed that combinations of isovaleric acid and androstenol were the guilty parties [56]. A subsequent patent taken out by Monell [57] contains detailed compositions and comprehensive references. 

---