Exploring Derivatives of Quinazoline Alkaloid l-Vasicine as Cap Groups in the Design and Biological Mechanistic Evaluation of Novel Antitumor Histone Deacetylase Inhibitors.

l-Vasicine is a quinazoline alkaloid with an electron dense ring and additional functionalities in its structure. Employing target oriented synthesis (TOS) based on in silico studies, molecules with significant docking scores containing different derivatives of l-vasicine as caps were synthesized. Interestingly, one molecule, i.e., 4a, which contained 3-hyroxypyrrolidine as a cap group and a six carbon long aliphatic chain as a linker was found to inhibit HDACs. 4a showed more specificity toward class I HDAC isoforms. Also 4a was found to be less cytotoxic toward normal cell lines as compared to cancer cell lines. 4a inhibited cancer cell growth and induced cell death by various mechanisms. However, 4a was found to induce cell death independent of ROS generation, and unlike many natural product based HDAC inhibitors, 4a was found to be nontoxic under in vivo conditions. Importantly, we for the first time report the possibility of using a 3-hydroxypyrrolidine cap for the synthesis of HDAC inhibitors with good potency.