and the use of tin (IV) chloride, capable of a 1,4-chelation, seem to impose their influence in the regiospecificringopening of 1a-g. The conformational analyses carried out on 2b and (1R,3R)-2e and (1R,3S)-2e clearly indicate that the N1(sp2)-C1-C2-C3 moiety tends to fold in a gauche conformation. The antitumour activities of compounds 2b-g were assessed against HEp human cells showing that 2c is 4-fold