Solid-Phase Synthetic Method For N-Alkyl-4-Alkylamino-6-Arylthieno [3,2-D]Pyrimidine-2-Carboxamide Derivatives

Herein, we describe a solid-phase synthetic method for synthesizing N-alkyl-4-alkylamino-6-arylthieno [3,2-d]pyrimidine-2-carboxamide derivatives. The derivatives consist of the biologically active 6-phenylthieno[3,2-d]pyrimidine scaffold. The template mediated synthetic strategy involving Suzuki coupling reactions between methyl 3-amino-5-bromothiophene-2-carboxylate and arylboronic acids afforded methyl 3-amino-5-arylthiophene-2-carboxylates. Cyclocondensation reactions involving methyl 3-amino-5-arylthiophene-2-carboxylates and methyl cyanoformate afforded esters, that when subjected to hydrolysis reactions yielded 6-aryl-4-oxo-3,4-dihydrothieno[3,2-d]pyrimidine-2-carboxylic acids (template compounds). These carboxylic acid templates were coupled with primary alkylamine-loaded acid-sensitive methoxybenzaldehyde (AMEBA) resins. The amide coupling reactions were followed by direct amination reactions mediated by benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate (BOP). The compounds were subsequently cleaved from the solid support, purified using the reverse phase-high performance liquid chromatography technique (RP-HPLC), and passed through a strong anion exchange (SAX) resin pretreated with water to yield the N-alkyl-4-alkylamino-6arylthieno[3,2-d]pyrimidine-2-carboxamide derivatives. The reaction conditions for the solid-phase transformations were optimized using a solution-phase model using 2,4-dimethoxybenzyl-protected isobutylamine as a reactant. 2,4-Dimethoxybenzyl-protected isobutylamine, and not AMEBA resin-loaded isobutylamine was used during the process. Substituent variation experiments were performed using 6-aryl-4-oxo-3,4-dihydrothieno[3,2-d]pyrimidine-2-carboxylic acids and a variety of primary and secondary amine building blocks. Additionally, we could include the Suzuki coupling step in a modified solid-phase synthetic sequence. (C) 2021 Elsevier Ltd. All rights reserved.