ABSTRACT
The absolute configuration of the alpha-methylbutyryl residue in (4R,5S,7S,8S,9S,10R,11R,2''S)-7-angeloyloxy-9-hydroxy-8-(alpha-methylbutyryloxy)-longipin-2-en-L-one and (4R,5S,7S,8R,10R,11R,2''S)-7-angeloyloxy-8-(alpha-methylbutyryloxy)- longipin-2-en-L-one was determined by chemical correlation with (S)-(+)-benzyl alpha-methylbutyrate prepared from authentic (S)-(+)-alpha-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 alpha-methylbutyryl esters found in nature and to reinforce the hypotheses on the biogenetic origin of these residues.
Subject(s)
Sesquiterpenes/chemistry , Sesquiterpenes/isolation & purification , Stevia/chemistry , Molecular Conformation , Molecular Structure , Plant Roots/chemistryABSTRACT
A series of six volatile sesquiterpenes (9-13 and 15) was prepared by thioketalization of (4R,5S,9S,10S,11S)-morel-2-en-1,7-dione (2) and of (4R,5S,7R,9R,11R)-moreli-2,10-dien-7-ol-1-one (3), followed by Raney-nickel desulfurization. The structures of the new substances were determined by 1D and 2D NMR including COSY, NOESY, HSQC, and HMBC experiments. The geometry of (3S,4R,5R,9S,10R,11S)-morelian-7-one (11), which exhibited an intense woody odor, was calculated by density functional theory at the B3LYP/6-31G level.
Subject(s)
Sesquiterpenes/chemical synthesis , Hydrolysis , Models, Molecular , Molecular Conformation , Molecular Structure , Odorants , Sesquiterpenes/chemistry , StereoisomerismABSTRACT
[structure: see text] The triterpenes 8,14-seco-oleana-8(26),13-dien-3beta-ol (1) and its acetyl derivative 2 were isolated from Stevia viscida and Stevia eupatoria, respectively. Their structures were elucidated by 2D NMR, including carbon-carbon connectivity experiments, and confirmed by X-ray diffraction analysis of ketone 3. The absolute configuration was determined by NMR analysis of the Mosher esters of 1. The biogenetic implications of the new substances are discussed.
Subject(s)
Oleanolic Acid/analogs & derivatives , Stevia/chemistry , Crystallography, X-Ray , Magnetic Resonance Spectroscopy , Models, Molecular , Molecular Conformation , TriterpenesABSTRACT
The molecular rearrangement of (1R,3S,4S,5S,7S,8R,9S,10R,11R)-7,8,9-triacetyloxylongipinan-1-ol (4) under acidic conditions afforded (1S,4R,5R,7S,8R,9S,10S)-7,8,9-triacetyloxyuruap-3(12)-ene (5), while 6, the C(3)-stereoisomer of 4, after two consecutive Wagner-Meerwein rearrangements followed by two 1,2-hydride migrations, afforded (4R,5R,7S,8S,9S,10S,11S)-7,8,9-triacetyloxyjiquilp-3(12)-ene (7), which possesses a new hydrocarbon skeleton. The structures of the new substances were elucidated by 1D and 2D NMR data in combination with X-ray diffraction analyses of the uruapane, longipinane, and jiquilpane derivatives 5, 6, and 14, respectively. Molecular modeling at the ab initio level was used to study the reaction mechanisms, while deuterium labeling was employed to confirm the C-C bond migrations and the hydride shifts.
