ABSTRACT
This study presents a first report on ruthenium-catalyzed asymmetric transfer hydrogenation (ATH) of levulinic acid (LA) to chiral γ-valerolactone (GVL). ATH of LA has been explored with Noyori's chiral catalyst (Ru-TsDPEN) in methanol solvent. Efficacy of ATH reaction of LA was investigated under different reactions conditions such as temperature, catalyst, and hydrogen donor concentration. The effect of various organic tertiary bases along with formic acid (FA) as a hydrogen donor was studied, and N-methylpiperidine with FA (1:1 molar ratio) was revealed as an efficient hydrogen donor for ATH of LA to GVL furnishing chiral GVL with complete conversion and 93% enantiomeric excess (ee). This operationally simple and mild ATH protocol was tested for practical applicability of ATH of LA obtained from biomass waste (rice husk and wheat straw) and furnished chiral GVL with 82% ee.
ABSTRACT
Homogeneous catalysts often show high activity and selectivity towards the various chemical transformations. Most of the transition metal-based active catalysts are expensive, rare, and have strict regulations for their use in pharmaceutical products. Hence, there is a requirement to develop suitable technologies for the practical separation and recycling of metal complex catalysts along with the sustainability of the process. This review focuses on the recent techniques used for the catalyst separation, their recovery, and recyclability of the homogeneous form of catalysts based on their economic compatibility and industrial applications. Various homogeneous catalysts have been reviewed on the basis of their support or media, active centres and recyclability aspects of the catalysts. This review gives brief insights into the varied examples of different recycling techniques utilized in the past 6-7â years.
ABSTRACT
The utility of a chiral Ru-prolinamide catalytic system has been demonstrated in one-pot synthesis of optically active ß-triazolylethanol and ß-hydroxy sulfone derivatives. The said methodology proceeds through asymmetric transfer hydrogenation of in situ formed ketones of the corresponding chiral products. Various chiral prolinamide ligands were screened, and ligand L6 with isopropyl groups substituted at the ortho position has shown excellent activity at 60 °C in aqueous medium producing up to 95% yield and 99.9% enantioselectivity.
ABSTRACT
BACKGROUND: Tooth is the hardest and chemically (except mineral contents) the most stable structure in the body, which makes teeth as the first-rate material for genetic and forensic investigations. Sex determination of skeletal remains forms an important part of archaeological and medicolegal examinations. Hence, the aim of the present study was to analyse the morphometric and dimensional variation between male and female in north Indian population using maxillary arch parameters. MATERIALS AND METHODS: Fifty male and fifty female patients of age group 18-35 years were randomly selected after taking detail history. All maxillary impressions were made with alginate and poured in type III dental stone. These casts were measured for maxillary inter-canine width, maxillary first inter-premolar width, anteroposterior palatal width and palatal depth using a digital vernier caliper and findings were correlated with sexual dimorphism. RESULTS: The maxillary inter-canine width, maxillary first inter-premolar width, and palatal depth showed a significant difference with P < 0.05 between the means of two populations. Anteroposterior palatal width showed the comparatively less significant difference between two populations. CONCLUSION: Among north Indian population, maxillary inter-canine width, maxillary first inter-premolar width, and palatal depth can be used for sex assessment. The anteroposterior palatal width parameter is comparatively less significant in sex determination.
ABSTRACT
Asymmetric transfer hydrogenation (ATH) of imines has been performed with variation in formic acid (F) and triethylamine (T) molar ratios in water. The F/T ratio is shown to affect both the reduction rate and enantioselectivity, with the optimum ratio being 1.1 in the ATH of imines with the Rh-(1S,2S)-TsDPEN catalyst. Use of methanol as a cosolvent enhanced reduction activity. A variety of imine substrates have been reduced, affording high yields (94-98%) and good to excellent enantioselectivities (89-98%). In comparison with the common azeotropic F-T system, the reduction with 1.1/1 F/T is faster.
Subject(s)
Ethylamines/chemistry , Formates/chemistry , Imines/chemistry , Imines/chemical synthesis , Water/chemistry , Hydrogenation , Molecular StructureABSTRACT
UNLABELLED: Oral cancer is one of the ten leading cancers of the world. In India, it is one of the common cancers and is an important public health problem. Tobacco plays significant role in etiology of oral squamous carcinoma. Tobacco which is chewed or smoked contains many alkaloids which are known carcinogens. Oral submucous fibrosis (OSMF) is a disease of the Indian subcontinent, which through immigration has a worldwide distribution. Betel nut chewing plays significant role in etiology of OSMF. The nut alkaloids have been shown experimentally to result in stimulation of collagen synthesis by fibroblasts in vitro, which can induce precancerous conditions. MATERIALS AND METHODS: The present study was undertaken to detect nitrate and nitrite factor in saliva of cases with oral carcinoma, OSMF and normal individuals without any habits and to determine whether increased salivary nitrate and nitrite level is significant in oral carcinoma and submucous fibrosis using biochemical parameters. CONCLUSION: We conclude that the major inducer of oral squamous cell carcinoma (OSCC) is exposure to tobacco. Recent studies have demonstrated that oxidative and nitrosative stress contributes to the development of oral carcinogenesis through deoxyribonucleic acid (DNA) damage. Salivary composition of OSCC patients is substantially altered with respect to free radical-involved mechanisms.
