Jonathan H. Marriott, Stephen Neidle, Zbigniew Matusiak, Vassilios Bavetsias, Ann L. Jackman, Camille Melin and F. Thomas Boyle
5-Aminoindane was converted in six steps to the cyclopenta[g]quinazoline ketone 13. Condensation of 13 with diethyl 4-aminobenzoyl-L-glutamate, followed by in situ reduction, produced the secondary amine 15. N-Propargylation of 15, followed by deprotection, gave the diacid 17 as a mixture of diastereoisomers. Treatment of 17 with the bacterial enzyme carboxypeptidase G2 resulted in removal of the L-glutamic acid residue from (6R)-17 to give a chromatographically separable mixture of the monoacid 18 and the antifolate 5 [(6S)-17], which was assayed as an inhibitor of thymidylate synthase (Kiapp = 3 nM). Treatment of isolated diacid 5 with carboxypeptidase G2 produced the monoacid 19 in ca. 98% enantiomeric excess. The (6S
) stereochemistry of compound 19 has been established by X-ray crystal structure determination of the amide derivative 24.