1,3-Dipolar cycloaddition of münchnones (mesoionic 1,3oxazolium-5-olates) 3 and 4 with 2-and 3-nitroindoles, 2nitrobenzo[b]furan, and 3-nitrobenzo[b]thiophene affords the corresponding pyrrolo[3,4-b]indoles, benzo[b]furo[2,3-c]pyrroles, and benzo[b]thieno[2,3-c]pyrroles, respectively, in one operation in good to excellent yields.
The effects of replacing L-pyroglutamic acid with the cyclopropane analogue 2,3-methanopyroglutamic acid (2,3-MeGlp) on conformation and enzymatic stability have been investigated in 2,3-MeGlp-NHMe and the novel thyrotropin releasing hormone (TRH) analogue [2,3-MeGlp1]-TRH by x-ray diffraction and nmr. While 2,3-MeGlp-NHMe adopts a folded conformation (small psi angle) in the solid state, several conformations are available to the molecule in solution. 1H-nmr of the diastereomeric mixture [(+/- )-2,3-MeGlp1]-TRH indicates a close orientation of the pyrrolidone and imidazole rings. The 2,3-MeGlp-His amide bond is considerably more stable to pyroglutamate aminopeptidase than the Glp-His bond in TRH.
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