Recent trends in whole cell and isolated enzymes in enantioselective synthesis

Modern synthetic organic chemistry has experienced an enormous growth in biocatalytic methodologies; enzymatic transformations and whole cell bioconversions have become generally accepted synthetic tools for asymmetric synthesis. This review details an overview of the latest achievements in biocatalytic methodologies for the synthesis of enantiopure compounds with a particular focus on chemoenzymatic synthesis in non-aqueous media, immobilisation technology and dynamic kinetic resolution. Furthermore, recent advances in ketoreductase technology and their applications are also presented

Asymmetric oxidation of sulfides

This review discusses synthesis of enantiopure sulfoxides through the asymmetric oxidation of prochiral sulfides. The use of metal complexes to promote asymmetric sulfoxidation is described in detail, with a particular emphasis on the synthesis of biologically active sulfoxides. The use of non-metal-based systems, such as oxaziridines, chiral hydroperoxides and peracids, as well as enzyme-catalyzed sulfoxidations is also examined

1,3-Dipolar cycloadditions of 2-thio-3-chloroacrylamides with nitrile oxides and nitrones

1,3-Dipolar cycloadditions of 2-thio-3-chloroacrylamides with nitrile oxides and nitrones is described. A series of novel isoxazolines are isolated from the nitrile oxide cycloadditions, whilst the isoxazolines generated from the nitrone cycloadditions undergo further ring opening to yield piperidines

Copper-catalyzed asymmetric oxidation of sulfides

Copper-catalyzed asymmetric sulfoxidation of aryl benzyl and aryl alkyl sulfides, using aqueous hydrogen peroxide as the oxidant, has been investigated. A relationship between the steric effects of the sulfide substituents and the enantioselectivity of the oxidation has been observed, with up to 93% ee for 2-naphthylmethyl phenyl sulfoxide, in modest yield in this instance (up to 30%). The influence of variation of solvent and ligand structure was examined, and the optimized conditions were then used to oxidize a number of aryl alkyl and aryl benzyl sulfides, producing sulfoxides in excellent yields in most cases (up to 92%), and good enantiopurities in certain cases (up to 84% ee)

1,3-Dipolar cycloadditions of 2-thio-3-chloroacrylamides with diazoalkanes

2-Thio-3-chloroacrylamides undergo 1,3-dipolar cycloadditions with diazoalkanes leading to a series of novel pyrazolines and pyrazoles. The mechanistic and synthetic features of the cycloadditions to the 2-thio-3-chloroacrylamides at both the sulfide and sulfoxide levels of oxidation are rationalised on the basis of the nature of the substituents

Diastereoselective sulfur oxidation of 2-thio-3-chloroacrylamides

Diastereoselective sulfur oxidation in 2-thio-3-chloroacrylamides is described. A range of chiral amine auxiliaries were incorporated in the β-chloroacrylamide, and the efficiency with which the stereochemistry was relayed to the sulfur centre during sulfoxidation was investigated. Diastereomeric ratios of up to 3.3:1 were achieved

Synthesis of enantioenriched sulfoxides

This review discusses strategies for the asymmetric synthesis of sulfoxides, compounds with many applications in stereoselective synthesis and in some cases with pharmaceutical application. The review describes asymmetric oxidation, including metal catalyzed and non-metal and biological oxidation processes, in addition to synthetic approaches via nucleophilic substitution of appropriately substituted precursors. Kinetic resolution in oxidation of sulfoxides to the analogous sulfones is also discussed; in certain instances, access to enantioenriched sulfoxides can be achieved via a combination of asymmetric sulfide oxidation and complementary kinetic resolution in sulfoxide oxidation

The Rising Light Curves of Type Ia Supernovae

We present an analysis of the early, rising light curves of 18 Type Ia supernovae (SNe Ia) discovered by the Palomar Transient Factory (PTF) and the La Silla-QUEST variability survey (LSQ). We fit these early data flux using a simple power-law $(f(t) = {\alpha\times t^n})$ to determine the time of first light $({t_0})$, and hence the rise-time $({t_{rise}})$ from first light to peak luminosity, and the exponent of the power-law rise ($n$). We find a mean uncorrected rise time of $18.98 {\pm} 0.54$ days, with individual SN rise-times ranging from $15.98$ to $24.7$ days. The exponent n shows significant departures from the simple 'fireball model' of $n = 2$ (or ${f(t) \propto t^2}$) usually assumed in the literature. With a mean value of $n = 2.44 {\pm} 0.13$, our data also show significant diversity from event to event. This deviation has implications for the distribution of 56Ni throughout the SN ejecta, with a higher index suggesting a lesser degree of 56Ni mixing. The range of n found also confirms that the 56Ni distribution is not standard throughout the population of SNe Ia, in agreement with earlier work measuring such abundances through spectral modelling. We also show that the duration of the very early light curve, before the luminosity has reached half of its maximal value, does not correlate with the light curve shape or stretch used to standardise SNe Ia in cosmological applications. This has implications for the cosmological fitting of SN Ia light curves.Comment: 19 pages, 19 figures, accepted for publication in MNRA

Synthesis and stereoselective oxidation of α-Thio-β- chloropropenyloxazolidin-2-ones

Investigation of the stereoselective reaction of α-thiopropanoyloxazolidin-2-ones with NCS to yield α-thio-β-chloropropenyloxazolidin-2-ones is described. Diastereoselective sulfur oxidation of the resulting α-thio-β-chloropropenyloxazolidin-2-ones is also discussed, with modest diastereocontrol achieved. However, through a combination of diastereoselective oxidation and subsequent kinetic resolution in the sulfoxide oxidation, diastereoselectivities of up to 94% de are achieved