Figure 2.

Synthesis of prototype RWJ-53052 (5). Reaction conditions (yield): a, BnNH₂, bis(2-oxo-3-oxazolidinyl)phosphinic chloride, CH₂Cl₂, 0°C (83%); b, 20% (vol/vol) piperidine in 1,4-dioxane (99%); c, Fmoc-4-methoxyphenylalanine, 1,3-diisopropylcarbodiimide, HOBt, CH₂Cl₂ (84%); d, 4-fluorobenzyl bromide, Cs₂CO₃, DMF; e, FeCl₃⋅6 H₂O, charcoal powder, Me₂NNH₂, MeOH, reflux (93% for 2 steps); f, 4-nitrophenylchloroformate, i-Pr₂NEt, CH₂Cl₂, −20°C—added 2 and warmed to 23°C (65%); g, 37% aqueous CH₂O, pyrrolidine, AcOH (63%); h, CF₃CO₂H/CH₂Cl₂ (97%). Abbreviations: Fmoc, 9-fluorenylmethoxycarbonyl; Pmc, 2,2,5,7,8-pentamethylchroman-6-sulfonyl; HOBt, 1-hydroxybenzotriazole; DMF, dimethylformamide.