Fig. 1: General synthetic scheme and structure of insulin analogs AcHI, PhacHI, AHI, and FHI.
From: Synthesis of a highly thermostable insulin by phenylalanine conjugation at B29 Lysine

a General synthetic scheme for the synthesis of active esters. b General scheme for the synthesis of newer insulin analogs. Condition A: Na2CO3/NaHCO3 buffer of pH10. Condition B: (1) Na2CO3/NaHCO3 buffer of pH10; (2) Trifluoroacetic acid. The asterisk denotes the point of attachment of carbon to the side chain amino group B29 Lys. Isolated yield of insulin analogs was mentioned in parentheses.