title: Design, synthesis, biological evaluation and X-ray crystal structure of novel classical 6,5,6-tricyclic benzo[4,5]thieno[2,3-d]pyrimidines as dual thymidylate synthase and dihydrofolate reductase inhibitors.
abstract: Classical antifolates (4-7) with a tricyclic benzo[4,5]thieno[2,3-d]pyrimidine scaffold and a flexible and rigid benzoylglutamate were synthesized as dual thymidylate synthase (TS) and dihydrofolate reductase (DHFR) inhibitors. Oxidative aromatization of ethyl 2-amino-4-methyl-4,5,6,7-tetrahydro-1-benzothiophene-3-carboxylate (±)-9 to ethyl 2-amino-4-methyl-1-benzothiophene-3-carboxylate 10 with 10% Pd/C was a key synthetic step. Compounds with 2-CH₃ substituents inhibited human (h) TS (IC₅₀ =0.26-0.8 μM), but not hDHFR. Substitution of the 2-CH₃ with a 2-NH₂ increases hTS inhibition by more than 10-fold and also affords excellent hDHFR inhibition (IC₅₀ = 0.09-0.1 μM). This study shows that the tricyclic benzo[4,5]thieno[2,3-d]pyrimidine scaffold is highly conducive to single hTS or dual hTS-hDHFR inhibition depending on the 2-position substituents. The X-ray crystal structures of 6 and 7 with hDHFR reveal, for the first time, that tricyclics 6 and 7 bind with the benzo[4,5]thieno[2,3-d]pyrimidine ring in the folate binding mode with the thieno S mimicking the 4-amino of methotrexate.
authors.affiliation: Division of Medicinal Chemistry, Graduate School of Pharmaceutical Sciences, Duquesne University, Pittsburgh, PA 15282, USA.
authors.forename: Xin
authors.initials: X
authors.lastname: Zhang
authors.forename: Xilin
authors.initials: X
authors.lastname: Zhou
authors.forename: Roy L
authors.initials: RL
authors.lastname: Kisliuk
authors.forename: Jennifer
authors.initials: J
authors.lastname: Piraino
authors.forename: Vivian
authors.initials: V
authors.lastname: Cody
authors.forename: Aleem
authors.initials: A
authors.lastname: Gangjee
mesh_terms: D018360:Crystallography, X-Ray; D015195:Drug Design; D004791:Enzyme Inhibitors / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D005493:Folic Acid Antagonists / Q000737:chemistry / Q000494:pharmacology; D006801:Humans; D008968:Molecular Conformation; D011743:Pyrimidines / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D013762:Tetrahydrofolate Dehydrogenase / Q000737:chemistry* / Q000378:metabolism; D013940:Thymidylate Synthase / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D005493:Folic Acid Antagonists; D011743:Pyrimidines; D013762:Tetrahydrofolate Dehydrogenase; D013940:Thymidylate Synthase; C030986:pyrimidine