New sulfur-containing alkaloids, 1 and 2, were isolated from the bark of Cassipourea guianensis and identified as 1-methyl-2-(4‘-hydroxy-1’, 2'-dithiolan-1'-oxo-3'-yl)-5-(4'-hydroxy-1″,2″-dithiolan-3″-yl)pyrrolidine and 1-methyl-2,5-bis-{4‘(4“)-hydroxy-1’(1”), 2'(2“)-dithiolan-1'(r')-oxo-3'(3”)-yl}pyrrolidine, respectively. © 1985, American Chemical Society. All rights reserved.