Dehydropeptides, hydrogenation

Synthesis of Peptides by Hydrogenation of Dehydropeptides. In addition to the interest in dehydropeptides in their own right, these compounds are also used to prepare non-proteinogenic peptides by simple reduction. For example, the electrochemical reduction of dehydropeptides derived from 2,3-dimethoxybenzaldehyde has been described. ... 

Dehydropeptides (21) were employed for the asymmetric hydrogenation, catalyzed by chiral rhodium complexes of the hydroxyproline derivative (13). It was reported that the stereoselectivity is satisfying (ds = 90-95 %)50). 

Some excellent reviews collect the early and recent literature with respect to typical complex-catalyzed reactions [5,6, 7, 8, 9,10,11,12]. Most of the water-soluble phosphines were synthesized by direct sulfonation of the phenyl group leading to mixtures of products. Sinou et al. [13] investigated the asymmetric hydrogenation of precursors of a-amino acids [ 14] and even of dehydropeptides... 

Proline r-butylester is the chiral inducer in hydrogenations of dehydrodipeptides and dehydropeptides under various conditions. The resulting amino acids form in 40% to 93% optical yields depending on the catalyst (finely divided Ni, Pd-C, PtOj), the temperature (- 30°C to RT), and the solvent. Experimental data indicate a steric course for this catalytic hydrogenation . 

Water-soluble mono- and diphosphines represent the major class of phosphines used in aqueous-phase homogeneous catalysis. However, some new types of water-soluble phosphines have been developed, including phosphines containing sugar substructures [31] or phosphonate chains [32], and chiral sulfonated phosphines for the asymmetric hydrogenation of dehydropeptides [33] and phosphines with amino acid moieties [59]. 

A discussion of asymmetric hydrogenation and hydrosilylation catalysed by Rh complexes highlights the effects of Hj pressure on the stereoselectivity and efficiency of typical chiral diphosphine ligands . Dehydropeptides Ac-ATyr(Ac)-(S)-Ala-Gly-OMe,... 

Asymmetric Hydrogenation of Amino-acids.—The conversion of dehydropeptides into optically active peptides has been studied in detail this year. The double asymmetric hydrogenation of (291) leads to A -acetyl-(S)-phenylalanyl-(S)-phenylalanine methyl ester (292) with a diastereoselectivity of 98 2 (Scheme 143). This approach has been applied to the synthesis of enkephalin and of... 

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