Design, synthesis and biological evaluation of brain penetrant benzazepine-based histone deacetylase 6 inhibitors for alleviating stroke-induced brain infarction.

Histone deacetylase 6 (HDAC6) has become a promising therapeutic target for central nervous system diseases due to its more complex protein structure and biological functions. However, low brain penetration of reported HDAC6 inhibitors limits its clinical application in neurological disorders. Therefore, the benzazepine, a brain-penetrant rigid fragment, was utilized to design a series of selective HDAC6 inhibitors to improve brain bioavailability. Various synthetic strategies were applied to assemble the tetrahydro-benzazepine ring, and 22 compounds were synthesized. Among them, compound 5 showed low nanomolar potency and strong isozyme selectivity for the inhibition of HDAC6 (IC50 = 1.8 nM, 141-fold selectivity over HDAC1) with efficient binding patterns like coordination with the zinc ion and π-π stacking effect. Western blot results showed it could efficiently transport into SH-SY5Y cells and selectively enhance the acetylation level of α-tubulin with a moderate effect on Histone H3. Notably, pharmacokinetic studies demonstrated that compound 5 (brain/plasma ratio of 2.30) had an excellent ability to penetrate the blood-brain barrier of C57 mice. In male rats with transient middle cerebral artery occlusion (MCAO), compound 5 significantly reduced the cerebral infarction from 21.22% to 11.47% and alleviated neurobehavioral deficits in post-ischemic treatment, which provided a strong rationale for pursuing HDAC6-based therapies for ischemic stroke.