Chemical synthesis of alpha-inhibin-92 by the thiocarboxyl segment coupling method.

The amino acid residue peptide, alpha-inhibin-92 (alpha-IB-92), has been synthesized by the thiocarboxyl segment strategy. Three segments were synthesized by the solid phase method, purified, and characterized: [GlyS34]-alpha-IB-92-(1-34) (I), CF3CO-[GlyS65]-alpha-IB-92-(35-65) (II), and Msc-alpha-IB-92-(66-92) (III). All were reacted with citraconic anhydride followed by removal of the Msc group in III to give Ia, IIa, and IIIa, respectively. Peptide IIIa was coupled to IIa by the silver nitrate/N-hydroxysuccinimide procedure and, after removal of uncoupled segments and the trifluoroacetyl group, Ia was coupled followed again by removal of uncoupled segments. Final deblocking to remove citraconyl groups was accomplished under exceptionally mild conditions in aqueous acetic acid. The synthetic product was identical to natural alpha-IB-92 in amino acid analysis, HPLC, gel electrophoresis, and tryptic mapping. The synthetic peptide was indistinguishable from natural alpha-IB-92 in a radioimmunoassay and in an in vitro mouse pituitary assay for measuring suppression of FSH release in the presence of LHRH.