Synthesis of thiazino[6,5- b]indole derivatives, analogues of the phytoalexin cyclobrassinin. A new method for preparation of 3-aminomethylindole

Abstract

An efficient non-reductive synthesis of 3-aminomethylindole ( 6 ) was developed from gramine ( 1 ) via 3-phthalimidomethylindole ( 2 ). The reactions of amine 6 with substituted methyl dithiobenzoates gave 3-(arylthiocarbonylaminomethyl)indoles. The Hugerschoff ring-closure reactions of the thiobenzamide intermediates ( 11a– f ) with phenyltrimethylammonium tribromide and subsequent basic treatment furnished 2-arylthiazino[6,5- b]indole derivatives ( 14a– f ). By use of the latter bromine source, the phytoalexin cyclobrassinin ( 8 ) was prepared in a considerably higher yield than described previously. The structures of the novel products were elucidated by IR, 1H and 13C NMR spectroscopy, including 2D-HMQC, 2D-HMBC and DEPT measurements.