Novel synthesis of CP-734432, an EP4 agonist, using Sharpless asymmetric dihydroxylation

Modular enantioselective synthesis of 8-aza-prostaglandin E1

We report herein for the first time the enantioselective synthesis of 8-aza-PGE1. The synthesis used the cross olefin metathesis reaction to connect the 5-vinyl-γ-lactam subunit, prepared from (R)-malic acid via the Ley's sulfone-based α-amidalkylation protocol (dr = 6.8:1), with the chiral pre-ω-chain. The latter was synthesized in high enantioselectivity from (E)-2-octenol by the Sharpless asymmetric epoxidation and the titanocene-mediated epoxide opening. This modular approach is quite concise and flexible, and requires only eight steps from commercially available reagents.

SmI2-mediated intermolecular coupling of γ-lactam N-α-radicals with activated alkenes: asymmetric synthesis of 11-hydroxylated analogues of the lead compounds CP-734432 and PF-04475270

We report, for the first time, the synthesis of 8-aza-analogues of PGE2. The SmI2-mediated cross coupling reactions of γ-lactam-hemiaminal 9, lactam 2-pyridyl sulfide 17, and lactam 2-pyridyl sulfone 18 with activated alkenes/alkyne were first developed, giving the corresponding γ-lactams in 49-78%, 45-75%, and 75-90%, respectively. The reactions of lactam 2-pyridyl sulfide and 2-pyridyl sulfone proceeded with ≥12:1 trans-diastereoselectivities. This represents the first intermolecular coupling reaction of the γ-lactam N-α-alkyl radicals of types B, B1, and B2 with activated alkenes. Two radical-based mechanisms were suggested. The asymmetric synthesis of the 11-hydroxylated analogue of the highly selective EP4 receptor agonist PF-04475270 (30), the 11-hydroxylated analogue of ocular hypotensive CP-734432 (31), compounds 35 and 36 have been achieved on the basis of this method.