The structure, absolute configuration, and preferred conformation, both in the solid state and in solution, of melledonal C (11 ), a A2*3-protoilludenese squiterpenoid from Armillaria mellea, have been established by a combination of X-ray and n.m.r. procedures. Ring A of the protoilludene skeleton was found in the crystal in a slightly twisted envelope conformation with C(10) displaced 0.55 A below the C(9), C(13), C(12), C(11) plane; ring B is a (7p,9c~)f lattened half-chair and ring c assumes a (4p,6P) highly puckered conformation. A strong intramolecular hydrogen bond between the 4-OH proton and the oxygen atom of 1 0-OH was evidenced in the solid state as well as in solution ( [2H,]acetone) using the SIMPLE 'H n.m.r. method (secondary isotope multiplet n.m.r. of partially labelled entities). Contrary to what is observed in solution, in the solid state there is no hydrogen bonding between the 3'-OH proton and the oxygen atom of the adjacent C02R group. The structure of melledonals A (9) and B (lo), and the absolute configuration at C(13) of melleolides C (6) and D (7) have also been elucidated by n.m.r. and chemical evidence.
SECONDARY MOULD METABOLITES. 19. STRUCTURE ELUCIDATION AND ABSOLUTECONFIGURATION OF MELLEDONAL-B AND MELLEDONAL-C, NOVEL ANTIBACTERIAL SESQUITERPENOIDS FROM ARMILLARIA-MELLEA - X-RAY MOLECULAR-STRUCTURE OF MELLEDONAL-C
MEILLE, STEFANO VALDO
1988-01-01
Abstract
The structure, absolute configuration, and preferred conformation, both in the solid state and in solution, of melledonal C (11 ), a A2*3-protoilludenese squiterpenoid from Armillaria mellea, have been established by a combination of X-ray and n.m.r. procedures. Ring A of the protoilludene skeleton was found in the crystal in a slightly twisted envelope conformation with C(10) displaced 0.55 A below the C(9), C(13), C(12), C(11) plane; ring B is a (7p,9c~)f lattened half-chair and ring c assumes a (4p,6P) highly puckered conformation. A strong intramolecular hydrogen bond between the 4-OH proton and the oxygen atom of 1 0-OH was evidenced in the solid state as well as in solution ( [2H,]acetone) using the SIMPLE 'H n.m.r. method (secondary isotope multiplet n.m.r. of partially labelled entities). Contrary to what is observed in solution, in the solid state there is no hydrogen bonding between the 3'-OH proton and the oxygen atom of the adjacent C02R group. The structure of melledonals A (9) and B (lo), and the absolute configuration at C(13) of melleolides C (6) and D (7) have also been elucidated by n.m.r. and chemical evidence.File | Dimensione | Formato | |
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Pub018 Arm mellea metab x-ray Nasini Perkins I 1988.pdf
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