Improved Schöllkopf construction of quaternary α-amino acids: efficient enantioselective synthesis of integrin LFA-1 antagonist BIRT-377

Recent Advances in the Synthesis of Hydantoins: The State of the Art of a Valuable Scaffold

The review highlights the hydantoin syntheses presented from the point of view of the preparation methods. Novel synthetic routes to various hydantoin structures, the advances brought to the classical methods in the aim of producing more sustainable and environmentally friendly procedures for the preparation of these biomolecules, and a critical comparison of the different synthetic approaches developed in the last twelve years are also described. The review is composed of 95 schemes, 8 figures and 528 references for the last 12 years and includes the description of the hydantoin-based marketed drugs and clinical candidates.

Stereodivergent synthesis of the LFA-1 antagonist BIRT-377 by porcine liver esterase desymmetrization and Curtius rearrangement

BIRT-377 was synthesized by enzymatic desymmetrization in conjunction with Curtius rearrangement, affording a key α-quaternary amine intermediate in high ee.

Complete analysis of the 1H and 13C NMR spectra of diastereomeric mixtures of (R,S- and S,S-)-3,6-dimethoxy-2,5-dihydropyrazine-substituted indoles and their conformational preference in solution

Complete analysis of the (1)H and (13)C NMR spectra obtained with and without a chemical shift reagent (Eu(fod)(3)), of bis-lactim ether 1 (Schöllkopf auxiliary) and monosubstituted 3- or 2-{(2R,5S or 2S,5S)-5-isopropyl-3,6-dimethoxy-2,5-dihydropyrazin-2-yl]methyl}-1H-indoles is presented using gradient-selected one-dimensional (1D) and two-dimensional NMR techniques, such as 1D TOCSY, 1D NOESY (DPFGSE NOE), gCOSY, NOESY, ROESY gHETCOR, gHSQC and gHMBC. The contour plot of the gCOSY spectrum of 1-10 revealed cross peaks arising from the five-bond coupling between the H2 and H5 resonances of the dihydropyrazine ring for syn- ((5)J(H2, H5) = 4-5.7 Hz) and for anti-isomers ((5)J(H2, H5) = 3.4-3.8 Hz). The magnitude of the coupling constant was utilized to distinguish between the syn- and the anti-isomers (diastereomers). The precise values of (n)J(HH) (n = 3, 4, 5, 6) coupling constants for the indole and 2,5-dihydropyrazine moieties deduced from the calculated NMR spectra were supported by 1D TOCSY and gCOSY experiments and gauge invariant atomic orbital (GIAO) calculations. The magnitude of the coupling constants ((5)J(H2, H5)) indicates that the dihydropyrazine ring exists in a boat conformation. In both isomers, the indole group adopts a 'folded' conformation in which one diastereotopic face is effectively shielded by the aromatic benzene ring of the indole. This is supported by gradient-selected 1D NOESY and 2D NOESY experiments. Theoretical calculations of the conformation were performed to support the through-space shielding effect of the aromatic indole moiety based on the DFT/GIAO calculated (1)H NMR data (chemical shifts and coupling constants) for 2-syn- and 2-anti-diastereomers in CDCl(3).

Diastereoselective synthesis of quaternary α-amino acids from diketopiperazine templates

Sequential enolate alkylations of (S)-N(1)-methyl-5-methoxy-6-isopropyl-3,6-dihydropyrazin-2-one and (S)-N(1)-p-methoxybenzyl-5-methoxy-6-isopropyl-3,6-dihydropyrazin-2-one proceed with excellent levels of diastereoselectivity (>90% de) affording quaternary alpha-amino acids in high enantiomeric excess (>98% ee) after deprotection and hydrolysis.