- Helical structures of cyclopentenebased α,α-disubstituted a-amino acid homopeptides
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The cyclopentene-based α,α-disubstituted a-amino acid Ac5c= and its homopeptides, up to nonapeptides, were synthesized. The side-chain cyclopentene was expected to become symmetric, the Ca-carbon to be puckered, and other Cβ, Cβ', C, C-carbons to be coplanar. As expected, side-chain cyclopentene conformations became symmetric and Ca-carbons were puckered. Conformational studies using FT-IR absorption, 1H NMR spectra, and X-ray crystallographic analyses revealed that Ac5c= homopeptides did not form a planar conformation, but assumed a 310-helical structure, similar to cyclopentane-based α,α-disubstituted a-amino acid homopeptides.
- Tanaka, Masakazu,Yakabi, Haruka,Nakatani, Haruki,Ueda, Atsushi,Doi, Mitsunobu,Oba, Makoto
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- Microwave assisted synthesis of spiro-2,5-diketopiperazines
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A general and efficient method for the synthesis of spiro-2,5-diketopiperazines (spiro-DKPs) is described. Cyclization of Boc-protected dipeptides containing spiro-amino acids by microwave assisted heating in water furnished the corresponding spiro-DKPs. The spiro-amino acids were prepared by combining stereoselective alkylation reactions using the Sch?llkopf methodology for amino acid construction with Grubbs ring-closing metathesis (RCM) methodology using ruthenium complexes. The RCM reactions and all subsequent transformations to the spiro-DKPs were run with microwave assisted heating, resulting in high yields and short reaction times for all steps.
- Jam, Fariba,Tullberg, Marcus,Luthman, Kristina,Gr?tli, Morten
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p. 9881 - 9889
(2008/02/11)
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- Synthesis of isoxazoline-substituted symmetrical diketopiperazines
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A synthesis of racemic isoxazoline substituted symmetrical diketopiperazines has been achieved by twice utilizing a diastereoselective 1,3-dipolar cycloaddition step - mediated by intermolecular hydrogen-bonds between the Boc-NH of 2 and the requisite nitrile oxide (RCN+-O-) - to control alkene face selectivity. Dehydrative cyclization of the amide-linked amino acid 6 delivered diketopiperazine 8.
- Park, Kyung-Ho,Olmstead, Marilyn M.,Kurth, Mark J.
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p. 1267 - 1270
(2007/10/03)
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- Diastereoselective Solid-Phase Synthesis of Novel Hydantoin- and Isoxazoline-Containing Heterocycles
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Exploiting 1,3-dipolar cycloaddition and carbanilide cyclization transformations, we have prepared novel spirocyclic isoxazoloimidazolidinedione heterocycles of generalized structures II and III on solid phase starting from Merrifield resin. Cyclopentanoid isoxazoloimidazolidinedione II was obtained with complete diastereoselectivity, and cyclopropanoid isoxazoloimidazolidinedione III was obtained as an ≈ 2:1 mixture of diastereomers.
- Park, Kyung-Ho,Olmstead, Marilyn M.,Kurth, Mark J.
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p. 6579 - 6585
(2007/10/03)
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