Solid-phase peptide synthesis has been refined to a stage where efficient preparation of long and complex peptides is now achievable. However, the postsynthesis handling of poorly soluble peptides often remains a significant hindrance to their purification and further use. Several synthetic schemes have been developed for the preparation of such peptides containing modifications to aid their solubility. However, these require the use of complex chemistry or yield non-native sequences. We describe a simple approach based on the use of penta-lysine "tags" that are linked to the C-terminus of the peptide of interest via a base-labile linker. After ready purification of the now freely solubilized peptide, the "tag" is removed by simple, brief base treatment giving the native sequence in much higher overall yield. The applicability of the method was demonstrated by the novel preparation of insulin glargine via solid-phase synthesis of each of the two chains--including the notoriously poorly soluble A-chain--followed by their combination in solution via regioselective disulfide bond formation. At the conclusion of the chain combination, the solubilizing peptide tag was removed from the A-chain to provide synthetic human glargine in nearly 10% overall yield. This approach should facilitate the development of new insulin analogues as well as be widely applicable to the improved purification and acquisition of otherwise poorly soluble synthetic peptides.
The success of the M(1)-selective muscarinic antagonist pirenzepine in preventing myopia development in animal models implicates a role for the M(1) receptor. However, the relatively high dose of pirenzepine required may indicate that the drug acts through another receptor subtype. This study examined whether the M(4)-selective antagonist, himbacine, could also prevent myopia. Daily intravitreal injections of himbacine inhibited the inducement of myopia in chick eyes in a dose- dependent manner. Doses < or = 200 microg caused no significant inhibition of induced myopia compared to controls (-13.7 +/- 2.3 vs -16.2 +/- 0.9D, ANOVA p = 0.37), whilst a dose of 800 microg almost completely inhibited the induced myopia (-2.4 +/- 2.0, p < 0.01). Findings demonstrate himbacine is effective at preventing the development of myopia in chick and implicates a role for the M4 receptor.
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