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

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, H-1 and C-13 NMR spectroscopy, including 2D-HMQC, 2D-HMBC and DEPT measurements. (c) 2005 Elsevier Ltd. All rights reserved.