Efficient total synthesis of insulin is important to enable the application of medicinal chemistry to the optimization of the properties of this important protein molecule. Recently we described ‘ester insulin’ – a novel form of insulin in which the function of the 35 residue C-peptide of proinsulin is replaced by a single covalent bond – as a key intermediate for the efficient total synthesis of insulin. Here we describe a fully convergent synthetic route to the ester insulin molecule from three unprotected peptide segments of approximately equal size. The synthetic ester insulin polypeptide chain folded much more rapidly than proinsulin, and at physiological pH. Both the D-protein and L-protein enantiomers of monomeric DKP ester insulin (i.e. [AspB10, LysB28, ProB29]ester insulin) were prepared by total chemical synthesis. The atomic structure of the synthetic ester insulin molecule was determined by racemic protein X-ray crystallography to a resolution of 1.6 Å. Diffraction quality crystals were readily obtained from the racemic mixture of {D-DKP ester insulin + L-DKP ester insulin}, whereas crystals were not obtained from the L-ester insulin alone even after extensive trials. Both the D-protein and L-protein enantiomers of monomeric DKP ester insulin were assayed for receptor binding and in diabetic rats, before and after conversion by saponification to the corresponding DKP insulin enantiomers. L-DKP ester insulin bound weakly to the insulin receptor, while synthetic L-DKP insulin derived from the L-DKP ester insulin intermediate was fully active in binding to the insulin receptor. The D- and L-DKP ester insulins and D-DKP insulin were inactive in lowering blood glucose in diabetic rats, while synthetic L-DKP insulin was fully active in this biological assay. The structural basis of the lack of biological activity of ester insulin is discussed.

About six years ago, almost simultaneously, three independent groups reported the synthesis of a novel class of dendritic molecules. These molecules were equipped with a focal trigger; reaction at the trigger initiated the fragmentation of the dendrimer to its building blocks in a domino-like manner with consequent release of at least two tail-units. We termed these molecules ''self-immolative dendrimers' ' and demonstrated their distinctive ability to achieve molecular amplification of the initial triggering signal. The unique amplification effect obtained by self-immolative dendrimers is useful in the fields of drug delivery systems and diagnostic applications. This highlight summarizes the design, function, and applications of this unique class of molecules.

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Background:Human proinsulin provides a model for studies of toxic protein misfolding. Results: Folding efficiency of proinsulin is controlled by stereochemistry at position B8. Conclusion: The sign of a single angle can facilitate or impede disulfide pairing. Significance: A monogenic diabetes syndrome suggests that insulin has evolved to the edge of non-foldability.

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