Synthesis, Odour Characteristics, and Antimicrobial Activity of Optically Active (<i>Z</i>)-7-Decen-4-olide and Its Derivatives

Abstract

The position of the carbon-carbon double bond also affects the odour characteristics in γ -lactones 7,8) . γ -Alkyllactones with relatively short sidechains, such as γ-octaand γ-nonalactone, have a coconutty aroma. Conversely, those with relatively long side chains, such as γ -undeca-and γ -dodecalactone, exhibit fruity notes 9) . Based on these observations, the side-chain length and the odour characteristics of γ -alkyllactones appear to be correlated. In this study, we synthesized optically active 1a and its derivatives (1b-1f) and investigate their odour characteristics as a function of the carbon-carbon double bond and side-chain length (Fig. 1) . Because lactones exhibit antimicrobial activities 10−12) , we previously reported the antimicrobial activities of optically active whisky and cognac lactones against S. aureus 13,14) . Although γ -alkyllactones are typically used in perfumes, these lactones (1a-1f) can be used in new applications if they Abstract: Six optically active (Z)-7-decen-4-olide derivatives (1a-1f) were synthesized in 99% enantiomeric excess using diastereomeric resolution. The odour properties of the racemic and optically active 1a-1f were evaluated in terms of their orthonasal aromas. All of the stereoisomers had different odour characteristics and thresholds. Decen-4-olides (1a-1c) had a strong fruity note, whereas undecen-4-olide (1d and 1e) and dodecen-4-olide (1f) had a strong green note. For 7-alken-4-olides (1a, 1d, and 1f), the (R)-enantiomer had a lower odour threshold than the (S)-enantiomer. In contrast, no difference in the odour threshold was observed for the enantiomers of the 8-alken-4-olides (1b and 1e). Furthermore, the antimicrobial activity against Escherichia coli (E. coli; ATCC 25922) and Staphylococcus aureus (S. aureus; ATCC 29213) were investigated. Although the no differences in the antimicrobial activity of the stereoisomers was observed, 1d and 1e showed slight antimicrobial activity against E. coli, whereas only 1f showed antimicrobial activity against S. aureus. No antimicrobial activity was exhibited by (R)-1f, whereas (S)-1f exhibited strong antimicrobial activity.