Practical preparation and deblocking conditions for N‐α‐(2‐(P‐biphenylyl)‐2‐propyloxycarbonyl)‐amino acid (N‐α‐Bpoc‐Xxx‐OH) derivatives

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Abstract
Reproducible preparations are given for salts of the following L‐amino acid derivatives: Bpoc‐Ala‐OH, Bpoc‐Arg(Mtr)‐OH, Bpoc‐Asn‐OH, Bpoc‐Asp(OtBu)‐OH, Bpoc‐Cys(Acm)‐OH, Bpoc‐Cys(S‐tBu)‐OH, Bpoc‐Gln‐OH, Bpoc‐Glu(OtBu)‐OH, Bpoc‐Gly‐OH, Bpoc‐Ile‐OH, Bpoc‐Leu‐OH, N‐α‐Bpoc‐Lys(ε‐Boc)‐OH, Bpoc‐Met‐OH, Bpoc‐Phe‐OH, Bpoc‐Pro‐OH, Bpoc‐Ser(OtBu)‐OH, Bpoc‐Thr(OtBu)‐OH, Bpoc‐Tyr‐OH, Bpoc‐Val‐OH. A study of the deblocking of N‐α‐Bpoc peptides in dichloromethane containing 0.5% trifluoroacetic acid revealed that a rapid equilb‐rium is established between the first‐formed monomeric alkene 2‐p‐biphenylylpropene and the hindered dimer 2,4‐bis(p‐biphenylyl)‐4‐methyl‐l‐pentene. Thioethers were found to be inefficient carbocation scavengers for the deblocking reaction. The most efficient scavengers were found to be thiophenol and benzyl mercaptan, and the following approximate reactivity order was established: benzyl mercaptan ∼ thiophenol 〉 indole 1,3‐dimethoxybenzene ∼ resorcinol 〉1,3,5‐trimethoxybenzene ∼ dimethyl sulfide ∼ thioanisole.