A series of conformationally constrained derivatives of glucagon-like peptide-1 (GLP-1) were designed and evaluated. By use of [Gly (8)]GLP-1(7-37)-NH2 (2) peptide as a starting point, 17 cyclic derivatives possessing i to i + 4, i to i + 5, or i to i + 7 side chain to side chain lactam bridges from positions 18 to 30 were prepared. The effect of a helix-promoting alpha-amino-isobutyric acid (Aib) substitution at position 22 was also evaluated. The introduction of i to i + 4 glutamic acid-lysine lactam constraints in c[Glu (18)-Lys (22)][Gly (8)]GLP-1(7-37)-NH2 (6), c[Glu (22)-Lys (26)][Gly (8)]GLP-1(7-37)-NH2 (10), and c[Glu (23)-Lys (27)][Gly (8)]GLP-1(7-37)-NH2 (11) resulted in potent functional activity and receptor affinities comparable to native GLP-1. Selected GLP-1 peptides were chemoselectively PEGylated in order to prolong their in vivo activity. PEGylated peptides [Gly (8),Aib (22)]GLP-1(7-37)-Cys ((PEG))-Ala-NH2 (23) and c[Glu (22)-Lys (26)][Gly (8)]GLP-1(7-37)-Cys ((PEG))-Ser-Gly-NH2 (24) retained picomolar functional potency and avid receptor binding properties. Importantly, PEGylated GLP-1 peptide 23 exhibited sustained in vivo efficacy with respect to blood glucose reduction and decreased body weight for several days in nonhuman primates.
Hepcidin is a four disulfide 25-residue peptide hormone which has a central role in the regulation of iron homeostasis. To support studies on hepcidin we have sought to establish reliable and robust synthetic methods for the preparation of correctly folded materials. While correctly-folded hepcidin has good aqueous solubility, we have found that its direct synthetic precursor, linear (reduced) hepcidin peptide, is resistant to solubilization, prone to precipitation at pH > or = 6, and thus difficult to fold efficiently. Attempts to directly fold either the crude or purified linear hepcidin peptide by air or DMSO oxidation methods under basic conditions were ineffective. However, addition of a glutathione redox pair system improved folding of purified linear hepcidin at mild basic pH (pH 7.5). Under acidic conditions, it was possible to oxidatively fold both crude and purified hepcidin using a polymer-supported oxidizing strategy. Peptide precipitation was also avoided under acidic conditions. Isolated folding yields of human hepcidin under acidic polymer-assisted conditions were superior to yields under basic folding conditions. These studies enabled identification of a reliable synthetic route for correctly-folded hepcidin.
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