The first total synthesis of oxazolomycin A, a structurally novel oxazole polyene γ-lactam/β-lactone antibiotic, is described. Key features include the stereocontrolled construction of the right-hand heterocyclic core by taking advantage of an In(III)-catalyzed Conia-ene type cyclization and the asymmetric synthesis of the left-hand segment starting with a Cinchona alkaloid-catalyzed cyclocondensation of an aldehyde with an acid chloride.
The total syntheses of (+)-inthomycin A, (+)-inthomycin B and (-)-inthomycin C, the oxazole-triene antibiotics isolated from Streptomyces sp., have been accomplished via the highly enantio- and stereoselective construction of the C1-C7 (iododienyl)aldol units by taking advantage of a Cinchona alkaloid-catalyzed asymmetric β-lactone synthesis and their isomerisation-free Stille coupling with (E)-5-(3-(tributylstannyl)allyl)oxazole.
The postnatal proliferation and maturation of insulin-secreting pancreatic β-cells are critical for glucose metabolism and disease development in adults. Elucidation of the molecular mechanisms underlying these events will be beneficial to direct the differentiation of stem cells into functional β-cells. Maturation of β-cells is accompanied by increased expression of MafA, an insulin gene transcription factor. Transcriptome analysis of MafA knockout islets revealed MafA is required for the expression of several molecules critical for β-cell function, including Glut2, ZnT8, Granuphilin, Vdr, Pcsk1 and Urocortin 3, as well as Prolactin receptor (Prlr) and its downstream target Cyclin D2 (Ccnd2). Inhibition of MafA expression in mouse islets or β-cell lines resulted in reduced expression of Prlr and Ccnd2, and MafA transactivated the Prlr promoter. Stimulation of β-cells by prolactin resulted in the phosphorylation and translocation of Stat5B and an increased nuclear pool of Ccnd2 via Prlr and Jak2. Consistent with these results, the loss of MafA resulted in impaired proliferation of β-cells at 4 weeks of age. These results suggest that MafA regulates the postnatal proliferation of β-cells via prolactin signaling.
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