- Inhibitors of human purine nucleoside phosphorylase. Synthesis of pyrrolo[3,2-d]pyrimidines, a new class of purine nucleoside phosphorylase inhibitors as potentially T-cell selective immunosuppressive agents. Description of 2,6-diamino-3,5-dihydro-7-(3-thienylmethyl)-4H-pyrrolo[3,2-d] pyrimidin-4-one. Sircar, J.C., Kostlan, C.R., Gilbertsen, R.B., Bennett, M.K., Dong, M.K., Cetenko, W.J. J. Med. Chem. (1992)