Collins Oxidation of Methyl (+)-13β-Abiet-8-en-18-oate and Absolute Configuration of Suaveolic Acid

Article abstract of DOI:10.1246/bcsj.55.527

The oxidation of methyl (+)-13β-abiet-8-en-18-oate with Collins reagent yielded nine oxidation products.Their structures were elucidated on the basis of spectroscopic and chemical data to be methyl (-)-14-hydroxy-7-oxoabieta-8,11,13-trien-18-oate (1percent yield), methyl (-)-11,14-dioxoabieta-8,12-dien-18-oate (1percent), methyl (+)-11-oxo-13β-abiet-8-en-18-oate (18percent), methyl (-)-8α,9α-epoxy-7-oxo-13β-abietan-18-oate (2percent), methyl(+)-7-oxoabieta-8,11,13-trien-18-oate (2percent), methyl (+)-11,14-dihydroxy-7-oxoabieta-8,11,13-trien-18-oate (2percent), methyl (+)-7,11-dioxo-13β-abiet-8-en-18-oate (17percent), methyl(+)-14-oxo-13β-abiet-8-en-18-oate (15) (4percent), and methyl (+)-7-oxo-13β-abiet-8-en-18-oate (23percent) respectively.It is noteworthy that oxygenation occurs not only at the C-7 and C-11 positions but also at the C-14 position.The oxygenated products obtained in this studies could be useful intermediates for the synthesis of the oxidized diterpenoids of abietane skeleton.To exemplify this, 15 was converted to methyl suaveolate and suaveolol.Hydrolysis of the former yielded suaveolic acid, thus confirming its absolute configuration to be 4R, 5R, 10S, 13S, and 14S.