Two novel optically active penam derivatives

The X-ray structure analyses of the two optically active penam derivatives, (2S,4S,5R,6S)-2-benzylcarbamoyl-6-bromo-3, 3-dimethyl-4-thia-1-azabicyclo[ 3.2.0]heptan-7-one 4-oxide hydrate, C15H17BTN2O3S . H2O, (I), and (5R)-3-be nzylimino-2-isopropylidene-4-thia-1-aza-bicyclo[3.2.0]heptan-7-one, C15H16N 2OS, (II), have been determined in order to ascertain their absolute config urations. Both compounds adopt the open-book conformation for the fused bet a-lactam and thiazolidine rings. The beta-lactam ring is in a distorted pla nar conformation, while the thiazolidine ring is in an envelope conformatio n. The pyramidalization effect of the N1 atom in both compounds has been ch aracterized by a displacement of the N atom from the plane of its substitue nts: the N atom is displaced 0.344 (5) and 0.350 (5) Angstrom in molecules A and B of compound (I) and 0.410(5) Angstrom in compound (II).