REVERSAL OF ABSOLUTE STEREOCHEMISTRY OF THE PYRROLO[2,1-B]QUINAZOLINEALKALOIDS VASICINE, VASICINONE, VASICINOL AND VASICINOLONE

The previously assigned 3R configuration of (-)-vasicinone has been re versed and this pyrrolo[2,1-b]quinazoline-9-one has been shown to have the 3S-configuration (3) on the basis of an X-ray diffraction study o f (+)-vasicinone hydrobromide. Likewise, the 3R stereochemistry as sig ned earlier to (-)vasicine (peganine) (1) on the basis of an X-ray ana lysis of its hydrochloride has also been reversed by reinvestigation o f the X-ray diffraction analysis of the hydrobromide. The absolute ste reochemistry of the alkaloids (+)-vasicinol (2) and vasicinolone (5) w hich have been interrelated, should also have the 3S-configuration. A study of the H-1 nmr spectroscopy of (-)-vasicine by the use of Mosher 's method using MTPA [alpha-methoxy-alpha-(trifluoromethyl)phenylaceti c acid] esters indicated an exception to this model for establishing t he absolute configuration.