(S)-2-((((9H-Fluoren-9-yl)methoxy)carbonyl)amino)-3-(((2-phenylacetamido)methyl)thio)propanoic acid

Fmoc-Cys(PhAcm)-OH for the Synthesis of H2 Relaxin

Yang, Xu, et al. Organic letters, 2016, 18(21), 5516-5519.

The reproductive hormone human relaxin-2 (H2 relaxin) regulates mammalian pregnancy as a crucial hormone while also having antifibrotic and vasodilatory effects. Liu et al. created a sequential process to generate disulfide bonds in insulin analogue synthesis by substituting iodine oxidation with a combination of penicillin G-acylase (PGA) labile thiol-protecting group Phacm and Ellman's reagent (5,5'-dithiobis(2-nitrobenzoic acid), DTNB). The procedure works separately from native structure to successfully produce insulin analogues with significantly decreased conformational stability.
To adapt this strategy for H2 relaxin, the synthesis of the A chain began with the coupling of Fmoc-Cys(Phacm)-OH to NovoSyn TGA resin under Mitsunobu conditions to minimize racemization. The side chains of other Cys residues in the A chain were protected as trityl (Trt) at positions A10 and A15, and tert-butyl (tBu) at position A11. Conventional methods were used for peptide chain assembly, followed by cleavage from the resin using a mixture of 95% trifluoroacetic acid (TFA), 2.5% water, and 2.5% triisopropylsilane (TIS). The crude peptide product was then purified by C8 RP-HPLC, yielding A-chain 2 at 23%.