Kinetic and structural studies on 'tethered' Ru(II) arene ketone reduction catalysts.

A series of kinetic and structural investigations on ruthenium-based catalysts for asymmetric transfer hydrogenation (ATH) of ketones are reported. A method is reported for monitoring the formation of ruthenium hydride species in real time using (1)H NMR spectroscopy.

An investigation into the tether length and substitution pattern of arene-substituted complexes for asymmetric transfer hydrogenation of ketones.

A series of Ru(II) catalysts were prepared and tested in the asymmetric transfer hydrogenation of ketones. The catalyst containing a "4-carbon" tether gave the fastest rates of ketone reduction. This is due to both increased rate of regeneration of hydride "Ru-H" and increased rate of ketone reduction.

3-Hydroxypyrrolidines from epoxysulfonamides and dimethylsulfoxonium methylide.

N-Tosyl-protected 3-hydroxypyrrolidines are prepared by reaction of dimethylsulfoxonium methylide with readily available epoxysulfonamides.

Copper-catalyzed synthesis of medium- and large-sized nitrogen heterocycles via N-arylation of phosphoramidates and carbamates.

[reaction: see text] We have developed an efficient method for the preparation of medium- and large-sized nitrogen heterocycles via copper-catalyzed intramolecular N-arylation of phosphoramidates and carbamates. Introduction of the phosphoryl group or tert-butoxycarbonyl at N-termini can improve intramolecular cyclization under copper catalysis, and the phosphoryl and tert-butoxycarbonyl can easily be removed under the mild conditions; thus, the convenient and efficient method is suitable for the preparation of medium- and large-sized nitrogen heterocycles.

Synthesis of sterically hindered peptide analogs using diphenyl phosphite as the coupling reagent.

Some model sterically hindered peptide analogs were synthesized with various yields using diphenyl phosphite as the coupling reagent under mild conditions. The experimental procedure is straightforward and the products are easily isolated. This method may be convenient and efficient for the synthesis of hindered peptides.

Synthesis of nucleoside N-phosphoamino acids and peptide formation.

Nucleoside N-phosphoamino acids were synthesized through Atherton-Todd reaction of nucleoside H-phosphonate with amino acids, and their structures were confirmed by NMR and ESI-MS. After nucleoside N-phosphoamino acid was incubated in anhydrous methanol at 40 degrees C for 72 h, di- to tetra-peptide derivatives were detected by ESI-MS, and their structures were further identified by multistage mass spectrometry. These and previously published studies in aqueous solution suggest that nucleoside N-phosphoamino acids could have been prebiotic precursors of oligopeptides.

Synthesis and electrospray ionization mass spectra of AZT/d4T boranophosphates.

New anti-HIV prodrugs, conjugates of AZT and d4T with boranophosphates, were prepared by the H-phosphonate method. Their structures were determined by negative ion electrospray ionization mass spectrometry (ESI-MS) in conjunction with tandem mass spectrometry (MS/MS). The fragmentation pathways were investigated, and most of the fragment ions contained the boranophosphate or phosphinate group.

Synthesis of serine/alanine conjugated 3',5'-TpT.

Serine and alanine phosphoramidates conjugates of 3',5'-TpT 4, 5 were synthesized. The corresponding serine phosphoamidate possesses some unique properties due to the presence of the side chain hydroxyl group.