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

The diastereoisomeric (+)‐[1,8‐ 14 C]‐(1' R ,6 R , S)‐α‐bisabolol ( 2a ) and (−)‐[1,8‐ 14 C]‐(1′S, 6R, S)‐α‐bisabolol ( 2b ) were synthesized by reaction of the Grignard compound of [1,6‐ 14 C]‐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 [ 14 C]‐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).