Scheme 2. Synthesis of β-hLH[C72–L121] by NCL Between β-hLH[Z72–D99] and β-hLH[C100–L121] Fragments.

Amino acid residues bearing acid-labile protecting groups shown in deep red, pseudoproline dipeptides shown in orange (underlined), Acm-protected Cys residues shown in purple, and thioester functionality shown in green. NCL buffer: guanidine·HCl (6 M), Na₂HPO₄ (0.2 M), tris(2-carboxyethyl)phosphine hydrochloride (TCEP·HCl) (0.02 M), 4-mercaptophenylacetic acid (MPAA) (0.2 M), aqueous TCEP solution (0.5 M), pH 7.2–7.4. Thz-deprotection buffer: MeONH₂·HCl (0.3 M), guanidine·HCl (6 M), pH 4.0–4.5. Cocktail B: 88% TFA, 5% H₂O, 5% phenol (PhOH), 2% triisopropylsilane (TIPSH).