An insulin analogue comprises an insulin B-chain polypeptide containing a Trp substitution at position B26 relative to the sequence of wild-type insulin. The insulin analogue may additionally comprise an OrnB29 substitution, a C-terminal extension of one or two basic amino acids such as Arg-Arg, a GlnB13 substitution, a GlyA21 substitution, a HisA8 or ArgA8 substitution, or a combination thereof. The insulin analogue may be formulated in the presence of zinc ions at a molar ratio of 2.2-10 zinc ions per six insulin analogue monomers. The molecular design is believed to stabilize the dimer interface of insulin (and its stable formulation as a zinc insulin hexamer) by means of aromatic amino-acid substitutions at position B26 of the B chain. The insulin analogs of the present invention may have two chains (A and B) as in mammalian insulins or may be engineered with a C domain (4-12 amino acids in length) to provide a single-chain. The TrpB26-stabilized zinc insulin hexamers complement and extend other molecular strategies to achieve protracted action on subcutaneous injection.