Structure-function studies on gastrointestinal hormones: I. Synthesis of secretin analogs and their biological and immunological properties

Syntheses by conventional procedures of the three analogs corresponding to the porcine secretin sequence crossed at position 6 by the N-terminal hexapeptide sequences of VIP, GIP, and glucagon are described, viz., Ala⁴,Val⁵-, Tyr¹,Ala²,Glu³-, and Gln³-secretin (VIP-SN, GIP-SN, and GLU-SN). The analog Phe¹,Phe²,Trp³,Lys⁴-secretin (SOMA-SN), designed on the basis of the surprising homology of the sequence portions 10–13 of somatostatin and 5–8 of secretin, was also prepared. Finally, the synthesis of N^α-3-(4-hydroxyphenyl)propionyl-β-alanyl-secretin (DATA-SN), a tracer suitable for secretin radioimmunoassay and as an N-terminus modified secretin analog, is reported. The analogs are compared, in terms of their biological and immunological properties in different assay systems, with pure synthetic secretin.