Dequaternization of curare bases with sodium thiophenoxide and ethanolamine

To prepare (+)-tubocurine and O,O-dimethyl-(+)-tubocurine, the commonly used dequaternization procedures with sodium theophenoxide and ethanolamine were investigated. The quaternary compounds were (+)-tubocurarine chloride and the chloride and iodide salts of O,O-dimethyl-(+)-chondocurarine. The results obtained with ethanolamine indicate that Hofmann elimination is a major pathway and that N-demethylation is minor. The elimination products of O,O-dimethyl-(+)-chondocurarine iodide with ethanolamine were identified as O,O-dimethyltubocurinemethine, O,O-dimethyltubocurineisomethine, and O,O-dimethyltubocurinedimethine. N-Demethylation was the primary reaction with sodium thiophenoxide. Thus, dequaternization of (+)-tubocurarine chloride with sodium thiophenoxide provided (+)-tubocurine which, on diazomethylation, yielded O,O-dimethyl-(+)-tubocurine, identical to the compound obtained by N-demethylation of O,O-dimethyl-(+)-chondocurarine chloride with the same reagent.