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- Lund, P E, et al.
(författare)
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Stimulation of insulin release by isosmolar addition of permeant molecules.
- 1992
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Ingår i: Molecular and Cellular Biochemistry. - 0300-8177 .- 1573-4919. ; 109:1, s. 77-81
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Tidskriftsartikel (refereegranskat)abstract
- Pancreatic beta-cells are known to respond to hyposmolar stress by releasing insulin. It was evident from perifusion studies using islet cells from ob/ob-mice mixed with polyacrylamide beads that a similar type of secretory response can be obtained by isosmolar addition of 10-25 mM of the rapidly penetrating urea molecule. There was no effect with hyperosmolar addition of urea. The urea-induced insulin release differed from the ordinary stimulation of secretion in not disappearing but being more pronounced after previous heating to 45 degrees C or removal of extracellular Ca2+. Isosmolar urea was exceptional as an insulin secretagogue in being effective also in the presence of the alpha 2-adrenergic agonist clonidine or when lowering the temperature to 24 degrees C. Further support for the idea that isosmolar addition of rapidly penetrating molecules induces insulin release was obtained by testing non-metabolizable glucose analogues. Whereas 25 mM 3-O-methyl-D-glucose doubled the secretory rate within 4 min, the non-permeant L-glucose had only a slight initial action. When not compensating for the alterations of the medium osmolarity 3-O-methyl-D-glucose was without effect. Although expansion of beta-cells cannot explain the existence of a pronounced initial secretory response to D-glucose it may under certain conditions contribute to the stimulatory effects of the sugar.
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- Wiktelius, Daniel, 1976, et al.
(författare)
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Peracid dependent stereoselectivity and functional group contribution to the stereocontrol of epoxidation of (E)-alkene dipeptide isosteres
- 2006
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Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020. ; 62:15, s. 3600-3609
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Tidskriftsartikel (refereegranskat)abstract
- Twelve Boc-protected phenylaianyl-phenylalanine and phenylalanyl-glycine trans-vinyl isosteres were epoxidised with magnesium monoperoxyphtalate hcxahydrate (MMPP) and trifluoroperacetic acid, and the results have been compared with those from earlier studies on epoxidations with m-CPBA. The alkenes were synthesised in high yields with high E/Z-selectivities using either the Julia or Schlosser reactions. The formation of threo isomers was favoured in all epoxidation reactions except with CF3CO3H on substrates containing two allylic/homoallylic functional groups directing the peracid to opposite faces of the alkene. The switch to erythro selectivity observed with CF3CO3H is suggested to ernanate from coordination to the allylic ester functionalities via hydrogen bond donation from the peracid. The other peracid reagents seem to be preferentially coordinated to the allylic carbamate function. The contribution of individual functional groups to the stereopreference was also investigated. (c) 2006 Elsevier Ltd. All rights reserved.
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