Synthesis, Modeling, and In Vitro Activity of (3‘S)-epi-K-252a Analogues. Elucidating the Stereochemical Requirements of the 3‘-Sugar Alcohol on trkA Tyrosine Kinase Activity

Utilizing our recently published semisynthetic approach to the (3'S)-K-252a diastereomer, we report the first synthesis of the (3'R)-10 diastereomer and a set of related epimers, with the goal of defining the stereochemical role of the 3'-sugar hydroxyl group on trkA tyrosine kinase activity and selectivity. (3'R)-10 displayed potent trkA inhibitory activity with an IC50 value of 4 nM. The corresponding deshydroxy epimer (3'S)-14 was 7-fold more potent than its 3'R counterpart (natural stereochemistry) with a trkA IC50 value of 3 nM and demonstrated >280-fold selectivity over PKC (IC50 = 850 nM). In cells, (3'S)-14 displayed potent inhibition of trkA autophosphorylation with an IC50 < 10 nM. Molecular modeling studies revealed that the 3'-OH, due to the inverted geometry, forms significant H-bonding interactions with Glu27 and Arg195, an interaction that is not attainable with the natural isomers.