Lactams of 1-amino-3-carboxylic acid cyclic compounds are produced in enantiomeric form, together with an enantiomer of the corresponding ring-opened amino-acid or ester, by reaction of the racemic lactam with a novel lactamase. The products are useful in the synthesis of chiral carbocyclic nucleotides. The enantiomer is preferrably 2-azabicyclo(2.2.1)hept-5-en-3-one. It is desirable to isolate the enantiomer comprising predominantly the (+) enantiomer and a residual amount of the (-) enantiomer, wherein the (+) enantiomer is present in an enantiomeric excess of at least about 88% over the (-) enantiomer or the enantiomer comprising predominantly the (-) enantiomer and a residual amount of the (+) enantiomer, wherein the (-) enantiomer is present in an enantiomeric excess of at least about 98% over the (+) enantiomer.