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. Author manuscript; available in PMC: 2014 Oct 27.

Published in final edited form as: J Am Chem Soc. 2013 Mar 11;135(11):4333–4363. doi: 10.1021/ja3109664

Scheme 4 — Proline editing alternative approach: direct modification immediately after coupling of Fmoc-Hyp-OH. Synthesis of the peptides Ac-TYP(4R-OBzNO₂)N-NH₂(3) (top) and Ac-TYP(4R-azidoacetate)N-NH₂(83) via direct acylation.^a

^a (a) 20% piperidine/DMF; (b) Fmoc-Asn(Trt)-OH, HBTU, DIPEA/DMF; (c) Fmoc-Tyr(OtBu)-OH, HBTU, DIPEA/DMF; (d) Fmoc-Thr(OtBu)-OH, HBTU, DIPEA/DMF; (e) 10% Ac₂O/pyridine. R^N′ = Ac-Thr(OtBu)-Tyr(OtBu)-, R^C′ = -Asn(Trt)-NHRink-Resin. R^N = Ac-Thr-Tyr-, R^C = -Asn-NH₂

^b Reaction was performed manually in a disposable fritted tube.