New reagent for oxidative phenol coupling. The transformation of the monocyclic spermine base (S)-dihydroxyverbacine to the bicyclic alkaloid (S,S,S)-aphelandrine by cell free extract of barley seedlings

The soluble protein fraction of barley seedlings (Hordeum vulgare, Graminea e) in the presence of O-2 stereoselectively catalyzes the intramolecular ph enol coupling of the monocyclic spermine base (S)-dihydroxyverbacine to the bicyclic aphelandrine in preparative yield. The expected microsomal-bond c ytochrome P-450 enzyme system does not contribute to this reaction. The nat ure of the involved biocatalyst still remains uncertain. The catalytic pote ntial of the cell free extract of barley seedlings suggests its possible us e as an efficient tool for large scale stereoselective chemoenzymatic synth esis of aphelandrine type alkaloids. (C) 2001 Elsevier Science Ltd. All rig hts reserved.