Synthesis of 2,4-Di-1-pyrrolidinyl-9H-pyrimido[4,5-b]indoles, Including Antiasthma Clinical Candidate PNU-142731A

Two syntheses are described for 1-[(2,4-di-1-pyrrolidinyl-9H-pyrimido[4,5-b]indol-9-yl)-acetyl]pyrrolidine hydrochloride (PNU-142731A), a clinical candidate in the asthma area. The route involving the initial regioselective addition of glycine ethyl ester to commercially available 2,4,6-trichloropyrimidine is particularly well-suited for large-scale operation, as it is short, proceeds in good yield, is operationally straightforward, and requires no chromatographic purification of intermediates.