General strategy for a short and efficient synthesis of 3-hydroxy-4-methylprolines (HMP)

The non-proteinogenic amino acid 3-hydroxy-4-methylproline (HMP) is an active constituent of some potent antimicrobials including echinocandins, nostopeptins, pneumocandins, sporiofungin and mulundocandins. A synthesis has been achieved in 10 steps with 29% overall yield; the Evans’ aldol reaction using Crimmins’ modified method was pivotal to the success of the strategy.     

Tevatron: Recent results and prospects at the upgrade

In this article, we review some of the recent results from CDF and DØ experiments at the Tevatron and their prospects at the upgrade. Among the topics discussed are top quark physics, electroweak physics, qcd physics and new physics beyond standard model.     

Use of a chiral surfactant for enantioselective reduction of a ketone

The influence of a chiral surfactant and a polymer-supported chiral additive on reduction of ketones using sodium borohydride will be described. Initial preparations involved methylation of (S)-leucinol to give (2S)-N , N-dimethyl-2-amino-4-methyl-1-pentanol (1) (67%). The chiral surfactant (2) was synthesized by reacting (1) with bromohexadecane (71%). The functionalized styrene for the polymer-supported chiral additive (5) was synthesized by reacting (1) with 4-vinylbenzyl chloride. Polymerization was carried out with 10% of the functionalized monomer (4), 5% cross-linking agent divinylbenzene, and 85% styrene with AIBN as the initiator. The activity of the chiral surfactant and polymeric additive were examined by using them as additives in a standard reduction of 2-pentanone with sodium borohydride to yield (R)- and (S)-2-pentanol (3) (20%). The resulting alcohol was analyzed by polarimetry (ee 9.5%) and also esterified with (2S)-methylbutyric acid prior to characterization by NMR. 13C NMR indicated an enantiomeric excess of 5.2% when the chiral surfactant was used, and 7% when the polymeric additive was used.     

Synthesis of cyclopentane building blocks via an intramolecular CH insertion reaction of a chiral pool derived α-diazo-γ-hydroxy-β-ketosulfone

A highly functionalized cyclopentanone building block 13 was prepared by a facile Rh-catalyzed intramolecular CH insertion reaction of an enantiopure α-diazo-γ-hydroxy-β-ketosulfone 12, in turn derived from an α-hydroxy acid 2. A cyclic γ-hydroxy vinyl sulfone 16 was also prepared from 13.     

Carbene-catalyzed enantioselective annulation of dinucleophilic hydrazones and bromoenals for access to aryl-dihydropyridazinones and related drugs

4,5-Dihydropyridazinones bearing an aryl substituent at the C6-position are important motifs in drug molecules. Herein, we developed an efficient protocol to access aryl-dihydropyridazinone molecules via carbene-catalyzed asymmetric annulation between dinucleophilic arylidene hydrazones and bromoenals. Key steps in this reaction include polarity-inversion of aryl aldehyde-derived hydrazones followed by chemo-selective reaction with enal-derived α,β-unsaturated acyl azolium intermediates. The aryl-dihydropyridazinone products accessed by our protocol can be readily transformed into drugs and bioactive molecules.

Polarity inversion of arylidene hydrazones to react with bromoenals via carbene organic catalysis is disclosed. The reaction enantioselectively affords 6-aryl-4,5-dihydropyridazinones and related drugs with proven commercial applications.     

Polyhydroxy pregnanes from Dregea volubilis

Three new polyhydroxy pregnanes named dregealol (1), volubilogenone (2) and volubilol (3) were isolated from the flowers of Dregea volubilis, and their structures elucidated from extensive 2D NMR analysis. The structure of volubilol (3) was confirmed by X-ray crystallographic studies. The known pregnane derivatives drevogenin D, iso-drevogenin P and 17α-marsdenin were also isolated.     

Regioselectivity in palladium-catalyzed C-H activation/oxygenation reactions

[reaction: see text] Palladium-catalyzed directed C-H activation/oxygenation reactions have been explored in a series of meta-substituted aryl pyridine and aryl amide derivatives. These transformations tolerate a diverse array of electron-donating and electron-withdrawing meta-substituents and generally proceed with high levels of regioselectivity for functionalization of the less sterically hindered ortho-C-H bond.     

A novel synthesis of vinyl esters from vinylversatate-10

Vinylversatate-10 (VV10)¹ has successfully been used to synthesise a large number of lower vinyl esters by transvinylation in presence of mercuric acetate and sulfuric acid. The synthesis of vinylhalo esters proceeds with more difficulty. It has been observed that neither Hg(OAc)₂ nor H₂SO₄ alone is capable of initiating the transvinylation. Furthermore, it has been found that a molar ratio 2:1 of VV10 to carboxylic acid is sufficient to drive the reaction to the right by continuous distillation of the vinyl ester formed, and as a result a high yield of vinyl ester is obtained. A mechanism for this reaction and for the formation of side products has been proposed.     

Metal complexes of sulphur-nitrogen chelating agents. Part 14. Nickel(II), palladium(II), copper(II), cobalt(II), and cobalt(III) complexes of the tetradentate schiff bases having ONNS donor sites

Summary Complexes of nickel(II), palladium(II), copper(II), cobalt(II), and cobalt(III) with methyl-2-(-salicylaldiminoethyl)-cyclopent-1-en-dithiocarboxylate (H₂L¹) and methyl-2-(-salicylaldiminoisopropyl)cyclopent-1-en-dithiocarboxylate (H₂L²) have been prepared. They contain the donor sites ONNS. The metal(II) ions from neutral, monomeric square planar chelate complexes. The cobalt(III) complexes [CoL¹-(H₂O)₂]X (X=Cl or ClO₄) appear to betrans-diaqua-species. All compounds have been characterized by a number of physico-chemical methods.     

Synthetic studies toward macrocidins: an RCM approach for the construction of the central cyclic core

The central macrocyclic core of the macrocidins was constructed using RCM as the key reaction. A preliminary investigation dealing with the key reactions, that is, the Dieckmann cyclization and the RCM, revealed that RCM of the β-ketoamide is better than RCM of the corresponding acyltetramic acid.