Absolute configuration of the α-methylbutyryl residue in longipinene derivatives from Stevia pilosa

Abstract The absolute configuration of the α-methylbutyryl residue in (4 R ,5 S ,7 S ,8 S ,9 S ,10 R ,11 R ,2″ S )-7-angeloyloxy-9-hydroxy-8-(α-methylbutyryloxy)-longipin-2-en-l-one and (4 R ,5 S ,7 S ,8 R ,10 R ,11 R ,2″ S )-7-angeloyloxy-8-(α-methylbutyryloxy)- longipin-2-en-l-one was determined by chemical correlation with ( S )-(+)-benzyl α-methylbutyrate prepared from authentic ( S )-(+)-α-methylbutyric acid. Both compounds were isolated from the hexane extracts of roots of Stevia pilosa Lag. together with four other longipinene derivatives. The developed correlation method is useful to ascertain the chirality of natural α-methylbutyryl esters found in nature and to reinforce the hypotheses on the biogenetic origin of these residues.