Biosynthese der Verrucarine und Roridine. Teil 5. Synthese von zwei Diastereoisomerenpaaren des [1,8‐14C]‐α‐Bisabolols und Versuche zu deren Einbau in Verrucarol Verrucarine und Roridine, 32. Mitteilung [1]

The diastereoisomeric (+)‐[1,8‐14C]‐(1'R,6R, S)‐α‐bisabolol (2a) and (−)‐[1,8‐14C]‐(1′S, 6R, S)‐α‐bisabolol (2b) were synthesized by reaction of the Grignard compound of [1,6‐14C]‐5‐bromo‐2‐methyl‐2‐pentene (12) with (+)‐(R)‐ and (−)‐(S)‐4‐acetyl‐1‐methyl‐1‐cyclohexene, (6a) and (6b) respectively. For the preparation of compound 12, cyclopropyl methyl ketone was treated with [14C]‐methyl magnesium iodide to form the carbinol 11, which was cleaved by HBr. Compounds 6a and 6b were synthesized from (+)‐(R)‐ and (−)‐(S)‐limonene, (4a) and (4b), via the derivatives 5a, 6a and 5b, 6b respectively. ‐ This synthesis established the absolute configuration at C(1′) of the natural α‐bisabolols: (R) for (+)‐α‐bisabolol and (S) for (−)‐α‐bisabolol. ‐ Feeding experiments with cultures of Myrothecium roridum and radioactive (+)‐(1′R, 6R, S)‐ and (−)‐(1′S, 6R, S)‐α‐bisabolol (2a) and (2b) gave negative results. These findings indicate that bisabolane derivatives are not intermediates in the biosynthesis of verrucarol (3).