Synthesis and evaluation of a new class of nifedipine analogs with T-type calcium channel blocking activity

We have synthesized a novel series of 18 dialkyl 1,4-dihydro-4-(2′alkoxy-6′-pentadecylphenyl)-2,6-dimethyl-3,5 pyddine dicarboxylates from anacardic acid, a natural compound found in cashew nut shells, and investigated their blocking action on L- and T-type calcium channels transiently expressed in tSA-201 cells. The IC₅₀ values for L-type calcium channel block obtained with the series ranged from 1 to ∼40 μM, with higher affinities being favored by increasing the size of the alkoxy group on the 4-phenyl ring and ester substituent in the 3,5 positions. A detailed analysis of the strongest L-type channel blocker of the series (PPK-12) revealed that block was poorly reversible and mediated an apparent speeding of the time course of inactivation. Moreover, in the presence of PPK-12, the midpoint of the steady state inactivation curve was shifted by 20 mV toward more hyperpolarized potentials, resulting in an increase in blocking efficacy at more depolarized holding potentials. Surprisingly, PPK-12 blocked T- and L-type calcium channels with similar affinities. One of the weakest L-type channel inhibitors (PPK-5) exhibited a T-type channel affinity that was similar to that seen with PPK-12, resulting in a 40-fold selectivity of PPK-5 for T- over L-type channels. Thus, dialkyl 1,4-dihydro-4-(2′alkoxy-6′-pentadecylphenyl)-2,6-dimethyl-3,5 pyridine dicarboxylates may serve as excellent candidates for the development of T-type calcium-channel specific blockers.