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The chemical modification of the 4-acetylamino group on the cycloserine moiety of lactivicin (1a) was carried out.The lactivicin derivatives (1d, k-p and w) having heterocyclic acylamino groups which have been often utillized in β-lactam antibiotics showed potent antibacterial activities. Ester prodrugs (7a-d) of lactivicin derivatives were also prepared in order to improve the bioavailability on oral administration. The pivaloyloxymethyl (POM) esters (7a and 7b) and 1-ethoxycarbonyloxyethyl (EOE) ester (7c) were found to have slightly improved protective effect in vivo compared with their parent compounds 1c and 1k.

Lactivicin, a new type of antibiotic having β-lactam-like activity, and its derivatives were synthesized starting from 4-benzyloxycarbonylamino-3-isoxazolidinones and 2-oxoglutaric acid.

Aza analogues of lactivicin (1), a recently discovered novel antibiotic, were prepared by an application of our earlier convenient synthesis of 1 and its derivatives. A 1-unsubstituted pyrazolidinone derivative bearing 2-aminothiazol-4-yl-(Z)-methoxyiminoacetyl group exhibited in vitro antibacterial activity.

A new type of 5, 6-cis-carbapenems (racemic) having a sulfonyl group in the C-6 side-chain were synthesized by employing the synthetic methodology reported in our previous papers, and an alternative stereocontrolled synthesis of these 5, 6-cis-carbapenems was achieved starting from 8-oxo-7-azabicyclo [4.2.0] oct-3-ene (14) via an intramolecular aldol condensation as the key step. Chiral 5, 6-cis-carbapenems were also synthesized from (1S, 6R) -8-oxo-7-azabicyclo [4.2.0] oct-3-ene (29), which was derived from cis-1, 2, 5, 6-tetrahydrophthalic anhydride. The carbapenems thus obtained proved to be highly stable to the mouse kidney homogenate, and most of them showed good antibacterial activity as well as potent β-lactamase inhibitory activity.