Volatile Organic Sulfur-Containing Constituents in Poncirus trifoliata (L.) Raf. (Rutaceae)

During our screening of plant materials to find new natural fragrance and flavor ingredients, we discovered two series of 3-sulfanylalkyl alkanoates in a peel extract of fruits of wild-growing Poncirus trifoliata (L.) Raf. (Rutaceae), a species closely related to Citrus . The two series belong to alkanoates of 3-methyl-3-sulfanylbutan-1-ol and 3-sulfanylhexan-1-ol, respectively, and thus are members of a family of natural molecules having in common a 1,3-positioned O,S moiety. The alkanoate residues comprise all even-numbered saturated fatty acids from C2 (acetate) to C18 (octadecanoate). Among the 20 sulfur-containing compounds identified, 14 are described for the first time as naturally occurring in a botanical species. Several cysteine- S -conjugates were synthesized as hypothetical precursors of the new volatile sulfur-containing constituents, where after S -(3-hydroxy-1,1-dimethylpropyl)- l -cysteine, S -[3-(acetyloxy)-1,1-dimethylpropyl]- l -cysteine, and S -[1-(2-hydroxyethyl)butyl]- l -cysteine were identified in the fruit peel. No cysteine- S -conjugates were detected in the fruit juice. Keywords: Poncirus trifoliata (L.) Raf.; 3-methyl-3-sulfanylbutan-1-ol; 3-methyl-3-sulfanylhexan-1-ol; 3-methyl-3-sulfanylbutyl alkanoates; 3-sulfanylhexyl alkanoates; cysteine- S -conjugates; natural occurrence; fragrance and flavor chemical