Asymmetric synthesis of 3-substituted proline chimeras bearing polar side chains of proteinogenic amino acids

The amino-zinc-ene-enolate cyclization reaction is a straightforward route to the synthesis of 3-substituted prolines. Herein we report the application of this reaction to the syntheses of proline chimeras of lysine, glutamic acid, glutamine, arginine, and serine. All these compounds were obtained in enantiomerically pure form and suitably protected for peptide synthesis.     

Synthetic approach to hypoxyxylerone,novel inhibitor of topoisomerase I

[reaction: see text] A potential route to the topoisomerase I inhibitor hypoxyxylerone is demonstrated by a highly convergent synthesis of the penta(O-methyl) derivative. The key step in the approach is an anionic homo-Fries rearrangement, little used to date in natural product synthesis and employed here for the first time with a dinaphthalenic substrate, to access the pentacyclic system of hypoxyxylerone.     

Deoxygenation of Nitrosobenzene by the Electrogenerated Pd<Subscript>3</Subscript>(dppm)<Subscript>3</Subscript>(μ<Subscript>3</Subscript>-CO) Cluster

The 2-electron reduction of the unsaturated Pd₃(dppm)₃(CO)²⁺ cluster ([Pd₃]²⁺) affords the highly reactive neutral cluster [Pd₃]⁰, which reacts with nitrosobenzene (PhNO) yielding the organic azoxybenzene product (PhN(O)NPh) via the formation of “triplet” nitrene “PhN”. The formation of [Pd₃(μ₃-O)] as a possible (relatively unstable) intermediate is also postulated based on MALDI-TOF findings, but not formally demonstrated. Concurrently, no reaction between [Pd₃]⁰ and OPPh₃ occurs. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users. This paper is dedicated to Professor Dieter Fenske.     

Thin-layer chromatography of ecdysteroids originated fromSilene otites L. (Wib.)

Summary Thin-layer chromatographic investigations of ecdysteroids have been carried out to monitor their isolation by column chromatography and droplet countercurrent chromatography as well as to control the homogeneity of the pure products. Isolation scheme and chemical structure of the 20-hydroxyecdysone-22-benzoate and that of three new ecdysteroid compounds, 2-deoxy-1,20-dihydroxyecdysone, 2-deoxyecdysone-22-acetate and 2-deoxy-20-hydroxyecdysone-22-acetate are also presented.     

Oxidation of aromatic and aliphatic triisopropylsilanylsulfanyls to sulfonyl chlorides: preparation of sulfonamides

A series of aromatic and aliphatic triisopropylsilanylsulfanyls were prepared and oxidized to the sulfonyl chlorides with KNO₃/SO₂Cl₂. The sulfonyl chlorides were characterized via their conversion to sulfonamides.     

Investigation of vapor-deposited amorphous ice and irradiated ice by molecular dynamics simulation

With the purpose of clarifying a number of points raised in the experimental literature, we investigate by molecular dynamics simulation the thermodynamics, the structure and the vibrational properties of vapor-deposited amorphous ice (ASW) as well as the phase transformations experienced by crystalline and vitreous ice under ion bombardment. Concerning ASW, we have shown that by changing the conditions of the deposition process, it is possible to form either a nonmicroporous amorphous deposit whose density (approximately 1.0 g/cm3) is essentially invariant with the temperature of deposition, or a microporous sample whose density varies drastically upon temperature annealing. We find that ASW is energetically different from glassy water except at the glass transition temperature and above. Moreover, the molecular dynamics simulation shows no evidence for the formation of a high-density phase when depositing water molecules at very low temperature. In order to model the processing of interstellar ices by cosmic ray protons and heavy ions coming from the magnetospheric radiation environment around the giant planets, we bombarded samples of vitreous ice and cubic ice with 35 eV water molecules. After irradiation the recovered samples were found to be densified, the lower the temperature, the higher the density of the recovered sample. The analysis of the structure and vibrational properties of this new high-density phase of amorphous ice shows a close relationship with those of high-density amorphous ice obtained by pressure-induced amorphization.     

First direct lithiation of 2-pyridylpiperazine on solid phase

[reaction: see text] The first direct lithiation of a pyridine derivative on solid phase has been realized. Metalation of polymer-bound 2-pyridylpiperazine with the BuLi-LiDMAE reagent followed by electrophilic quenching and subsequent cleavage provided a range of new useful C-6 substituted 2-piperazinylpyridines.