3GI2:
reference: Design, synthesis, and X-ray crystal structure of classical and nonclassical 2-amino-4-oxo-5-substituted-6-ethylthieno[2,3-d]pyrimidines as dual thymidylate synthase and dihydrofolate reductase inhibitors and as potential antitumor agents., Gangjee A, Li W, Kisliuk RL, Cody V, Pace J, Piraino J, Makin J, J Med Chem. 2009 Aug 13;52(15):4892-902. PMID: 19719239

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