Solid-phase synthesis of 2-substituted 4-amino-7-oxo-5,6,7,8-tetrahydropyrido[2,3-d]pyrimidines: an example of cyclization-assisted cleavage.

An efficient solid-phase synthesis of 2-substituted 4-aminopyrido[2,3-d]pyrimidines 12 by cyclization-assisted cleavage from resin is reported. The procedure starts by solid supporting an alpha,beta-unsaturated acid 8 to the Wang resin 13 by using DCC and 4-DMAP in THF. The resulting alpha,beta-unsaturated ester 14 is converted to the Michael adduct by treatment with malononitrile in NaOMe/THF. Such Michael addition constitutes the first example of a Michael reaction with malononitrile in solid-phase. Finally, the Michael adducts 15 are treated with an amidine system in MeOH to yield the corresponding pyridopyrimidines 12. Compounds 12 present three diversity centers R1, R2 and G. Having validated the chemistry on solid support, a 40-membered combinatorial library was obtained using this protocol.