Synthesis, Enantiomeric Resolution and Biological Evaluation of HIV Capsid Inhibition Activity for Racemic, (S)- and (R)-PF74.

PF74 is a capsid-targeting inhibitor of HIV replication that effectively perturbs the highly sensitive viral uncoating process. A lack of information regarding the optical purity (enantiomeric excess) of the single stereogenic centre of PF74 has resulted in ambiguity as to the potency of different samples of this compound. Herein is described the synthesis of enantiomerically enriched (S)- and (R)-PF74 and further enrichment of the samples (≥98%) using chiral HPLC resolution. The biological activities of each enantiomer were then evaluated, which determined (S)-PF74 (IC50 1.5 µM) to be significantly more active than (R)-PF74 (IC50 19 µM). Computational docking studies were then conducted to rationalise this large discrepancy in activity, which indicated different binding conformations for each enantiomer. The binding energy of the conformation adopted by the more active (S)-PF74 (ΔG = -73.8 kcal/mol) was calculated to be more favourable than the conformation adopted by the less active (R)-enantiomer (ΔG = -55.8 kcal/mol) in agreement with experimental observations.