Seven title compounds 12a–g and the (S)-prolinate analogue 13 were prepared in five steps from 2-nitrobenzoic acid (7). Reduction of the nitro group followed by derivatization of the so formed ...anilines 14 gave the N-alkyl-(15a–c), N-acyl-(16a,b and 19), and N-vinyl derivative 20. NMR spectra of (S)-alanine and (S)-proline derived compounds 12, 13, 14–16, 19, and 20 exhibited two sets of signals corresponding to pairs of conformational diastereomers. The free energy barriers of rotation, ΔG ‡ 298 = 82–86 kJ mol–1, were determined by 1H NMR for 12a, 12d, 12f, and 12g and evaluated by DFT calculations.
Vinylogous peptides 3 with a vinyl fragment inserted into the peptide C–N bond were prepared from ynones 6 and enaminones 7 that are easily available from Boc‐protected α‐amino acids 4. Coupling at ...the C terminus was achieved by 1,4‐addition of amino esters 5 to the C≡C bond in 6 or by substitution of the NMe2 group in 7 to give N‐terminal vinylogues 3a–p. Coupling at the N terminus of 3 and 7, in contrast, required temporary protection of the acidolytically labile enamino moiety. Thus, cyclization of 6 or 7 with hydroxylamine, removal of the Boc group with HBr–AcOH, acylation of free amine 10 with BocGlyOH (4a), and hydrogenolytic deprotection of the enamino moiety in the presence of GlyOMe (5a) led to tripeptides 3q–s with vinylogous amide as the central building block.
Vinylogous peptides with a C=C fragment inserted into a peptide C–N bond are prepared from ynone building blocks that are easily available from Boc‐protected α‐amino acids. Coupling at the C terminus is achieved by 1,4‐addition of an α‐amino ester, whereas coupling at the N terminus requires temporary protection of the enaminone moiety by transformation into an isoxazole derivative.
A series of (S)-1-(pyrimidin-4-yl)-, and regioisomeric (S)-1-(pyrazolo1,5-apyrimidin-7-yl)-, and (S)-1-(pyrazolo1,5-apyrimidin-5-yl)ethan-1-amines were prepared by cyclisation of ...(S)-N-Boc-alanine-derived ynone with N,N-1,3-dinucleophiles, such as amidines and α-aminoazoles, followed by acidolytic removal of the Boc group. Stereoselective catalytic hydrogenation of (S)-1-(pyrazolo1,5-apyrimidin-7-yl)ethanamines lead to saturation of the pyrimidine ring to afford ~4:1 mixture of diastereomeric 4,5,6,7-tetrahydropyrazolo1,5-apyrimidines. The structures of novel compounds were elucidated with NMR.
Parallel screening of suitable reaction conditions for Cu(I)-catalyzed 3+2 cycloadditions of (1Z,4R*,5R*)-4-benzoylamino-1-benzylidene-5-phenyl-3-oxopyrazolidin-1-ium-2-ide (1a) to methyl propiolate ...(2) has established that this reaction proceeds smoothly at room temperature in acetonitrile in the presence of CuI and Hünig’s base. The optimized reaction conditions were then applied in regio- and stereo-selective 1,3-dipolar cycloadditions of racemic azomethine imines 1a-e to tert-butyl (S)-(3-oxopent-4-yn-2-yl)carbamate (6) leading to mixtures of diastereomeric non-racemic chromatographically separable cycloadducts 7a-d, 7'a-d, 8e, and 8'e. The structures of the products were confirmed by NMR spectroscopy.
A series of (S)-1-(pyrimidin-4-yl)-, and regioisomeric (S)-1-(pyrazolo1,5-apyrimidin-7-yl)-, and (S)-1-(pyrazolo1,5-apyrimidin-5-yl)ethan-1-amines were prepared by cyclisation of ...(S)-N-Boc-alanine-derived ynone with N,N-1,3-dinucleophiles, such as amidines and α-aminoazoles, followed by acidolytic removal of the Boc group. Stereoselective catalytic hydrogenation of (S)-1-(pyrazolo1,5-apyrimidin-7-yl)ethanamines lead to saturation of the pyrimidine ring to afford ~4:1 mixture of diastereomeric 4,5,6,7-tetrahydropyrazolo1,5-apyrimidines. The structures of novel compounds were elucidated with NMR.
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Provider: - Institution: - Data provided by Europeana Collections- All metadata published by Europeana are available free of restriction under the Creative Commons CC0 1.0 Universal Public Domain ...Dedication. However, Europeana requests that you actively acknowledge and give attribution to all metadata sources including Europeana
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