The octadecapeptide corresponding to the entire amino acid sequence of equine β-melanocyte-stimulating hormone (MSH) was synthesized by assembling 4 subunits ; Z (OMe)-Asp (OBzl)-Glu (OBzl)-Gly-OH (I), Z (OMe)-Pro-Tyr-Lys (Z)-Met-NHNH2 (II), Z (OMe)-Glu (OBzl)-His-Phe-Arg (Tos)-Trp-Gly-OH (III), Z (OMe)-Ser-Pro-Arg (Tos)-Lys(Z)-Asp (OBzl)2 (IV), followed by deblocking of all protecting groups with hydrogen fluoride. The in vivo MSH activity of synthetic equine β-MSH was found equivalent to that of synthetic human β-MSH (in vitro activity, 6.2×109 MSH unit/g).
