Minimizing Mitogenic Potency of Insulin Analogues Through Modification of a Disulfide Bond.

The mechanisms by which insulin activates the insulin receptor to promote metabolic processes and cellular growth are still not clear. Significant advances have been gained from recent structural studies in understanding how insulin binds to its receptor. However, the way in which specific interactions lead to either metabolic or mitogenic signalling remains unknown.

Probing the correlation between insulin activity and structural stability through introduction of the rigid A6-A11 bond.

The development of fast-acting and highly stable insulin analogues is challenging. Insulin undergoes structural transitions essential for binding and activation of the insulin receptor (IR), but these conformational changes can also affect insulin stability. Previously, we substituted the insulin A6-A11 cystine with a rigid, non-reducible C=C linkage ("dicarba" linkage).

Insulin in motion: The A6-A11 disulfide bond allosterically modulates structural transitions required for insulin activity.

The structural transitions required for insulin to activate its receptor and initiate regulation of glucose homeostasis are only partly understood. Here, using ring-closing metathesis, we substitute the A6-A11 disulfide bond of insulin with a rigid, non-reducible dicarba linkage, yielding two distinct stereo-isomers (cis and trans). Remarkably, only the cis isomer displays full insulin potency, rapidly lowering blood glucose in mice (even under insulin-resistant conditions).

Dicarba analogues of α-conotoxin RgIA. Structure, stability, and activity at potential pain targets.

α-Conotoxin RgIA is both an antagonist of the α9α10 nicotinic acetylcholine receptor (nAChR) subtype and an inhibitor of high-voltage-activated N-type calcium channel currents. RgIA has therapeutic potential for the treatment of pain, but reduction of the disulfide bond framework under physiological conditions represents a potential liability for clinical applications. We synthesized four RgIA analogues that replaced native disulfide pairs with nonreducible dicarba bridges.

Dicarba α-conotoxin Vc1.1 analogues with differential selectivity for nicotinic acetylcholine and GABAB receptors.

Conotoxins have emerged as useful leads for the development of novel therapeutic analgesics. These peptides, isolated from marine molluscs of the genus Conus, have evolved exquisite selectivity for receptors and ion channels of excitable tissue. One such peptide, α-conotoxin Vc1.

Synthesis, conformational analysis and biological properties of a dicarba derivative of the antimicrobial peptide, brevinin-1BYa.

Brevinin-1BYa (FLPILASLAAKFGPKLFCLVTKKC), first isolated from skin secretions of the frog Rana boylii, displays broad-spectrum antimicrobial activity and potent haemolytic activity. This study investigates the effects on conformation and biological activity of replacement of the intramolecular disulphide bridge in the peptide by a non-reducible dicarba bond. Dicarba-brevinin-1BYa was prepared by microwave irradiation of [Agl(18),Agl(24)]-brevinin-1BYa (Agl = allylglycine) in the presence of a second generation Grubbs' catalyst.

Role of the intra-A-chain disulfide bond of insulin-like peptide 3 in binding and activation of its receptor, RXFP2.

INSL3 is a member of the insulin-IGF-relaxin superfamily and plays a key role in male fetal development and in adult germ cell maturation. It is the cognate ligand for RXFP2, a leucine-rich repeat containing G-protein coupled receptor. To date, and in contrast to our current knowledge of the key structural features that are required for the binding of INSL3 to RXFP2, comparatively little is known about the key residues that are required to elicit receptor activation and downstream cell signaling.

Regioselective formation of interlocked dicarba bridges in naturally occurring cyclic peptide toxins using olefin metathesis.

Bis-dicarba analogues of native dicystine-containing alpha-conotoxin Rg1A, an analgesic peptide isolated from cone snail venom, were constructed on resin using a regioselective metathesis-hydrogenation strategy.

Solid phase synthesis and structural analysis of novel A-chain dicarba analogs of human relaxin-3 (INSL7) that exhibit full biological activity.

Replacement of disulfide bonds with non-reducible isosteres can be a useful means of increasing the in vivo stability of a protein. We describe the replacement of the A-chain intramolecular disulfide bond of human relaxin-3 (H3 relaxin, INSL7), an insulin-like peptide that has potential applications in the treatment of stress and obesity, with the physiologically stable dicarba bond. Solid phase peptide synthesis was used to prepare an A-chain analogue in which the two cysteine residues that form the intramolecular bond were replaced with allylglycine.

Metathesis assisted synthesis of cyclic peptides.

Installation of reversible, metathesis-active tethers into linear peptide sequences can be used to promote formation of cyclic peptide amides and esters.

Structure and activity of (2,8)-dicarba-(3,12)-cystino alpha-ImI, an alpha-conotoxin containing a nonreducible cystine analogue.

The alpha-conotoxins are potent and selective antagonists of nicotinic acetylcholine receptors (nAChR). Exploitation of these and other peptides in research and clinical settings has been hampered by the lability of the disulfide bridges that are essential for toxin structure and activity. One solution to this problem is replacement of cystine bridges with nonreducible dicarba linkages.

Microwave-assisted RCM for the synthesis of carbocyclic peptides.

Microwave irradiation dramatically improves the efficiency of ring closing metathesis (RCM) reactions of resin-attached peptides and the technology is illustrated by the highly selective synthesis of dicarba analogues of alpha-conotoxin IMI.