A concise synthesis of anti-viral agent F-ddA, starting from (S)-dihydro-5-(hydroxymethyl)-2(3H)-furanone

Anti-HIV agent β-F-ddA (1) has been synthesized starting from readily available non-sugar, (S)-(+)-Dihydro-5-(hydroxymethyl)-2-(3H)-furanone (4). A highly syn-stereoselective fluorination of the hydroxy lactone 2 generates the key intermediate fluorolactone 5 in a short and concise synthetic sequence. Reduction of 5 followed by bromination generates the aglycon which is glycosylated to generate F-ddA by amination and deprotection. Steric bulk of the 5-protecting group has minimal effect on the steric course of glycosylation.     

Synthesis of D-D4FC, a biologically active nucleoside via an unprecedented palladium mediated Ferrier rearrangement-type glycosidation with an aromatization prone xylo-furanoid glycal

D-D4FC (1) is an anti-HIV agent currently under phase II clinical trial (Pharmaset Inc). Its molecular architecture is suitable for a Ferrier rearrangement kind of operation on a furanoid glycal to fix the position of the double bond and the relative stereochemistry. Despite the fact that classical Ferrier rearrangement does not work on furanoid glycals, a palladium mediated modified protocol has been developed for the glycosidation of an aromatization prone xylo-furanoid glycal (5) for the synthesis of D-D4FC.     

Chemometric analysis of EDXRF measurements from fossil bone

Bone chemistry is an important source of biological and environmental information. Elemental compositions of archaeological and fossil bone have granted insight into the diets of ancient humans and other animals, as well as informing about the burial conditions of bone. Chemical studies of ancient bone can be performed non‐destructively with portable energy‐dispersive X‐ray fluorescence (EDXRF) spectrometers, which is particularly advantageous for on‐site analyses of museum specimens. Portable EDXRF instruments carry some analytical disadvantages, however, which may result in reduced precision or accuracy. Analytical shortfalls may be overcome by analysing inter‐sample trends in EDXRF spectral data instead of reported concentration measurements. We investigated the utility of statistically treating handheld EDXRF spectra from fossil bone and teeth, specifically the normalisation and mean centering of spectral data before principal component analysis. Fossil bone and tooth specimens were sourced from two Pleistocene localities in the Western Cape of South Africa, Swartklip 1 and Elandsfontein Main. Samples from the two localities could be distinguished using principal component score values, and coefficient loadings allowed chemical interpretation of the score clusters. Swartklip 1 samples were associated with elevated concentrations of Ca, indicating an additional Ca‐bearing mineral (i.e. calcite), whereas Elandsfontein Main samples were associated with elevated Fe and Sr concentrations. Fossil bone chemistry could be related to groundwater percolation through the sedimentary matrices of each locality. The methodology behind the case study presented here could readily be applied elsewhere and would be particularly useful to handheld EDXRF studies of museum specimens. Copyright © 2011 John Wiley & Sons, Ltd.     

A chemoselective aniline-chloropyrimidine coupling in a competing electrophilic environment

A highly chemoselective substitution on 4-amino-6-chloropyrimidine ring system having a competing aldehyde functionality has been realized with anilines which produces 4, 6-diaminopyrimidine-5-carbaldehyde in high yield. The reaction may involve the intermediacy of imines. A variety of aromatic amines participate in this reaction successfully to generate diaminopyrimidine aldehydes in moderate to high yield.     

A facile one-pot synthesis of acyclic β-enamino ketones, an important class of versatile synthetic intermediates

A one-pot sequential process consisting of nucleophilic substitution of the lithiated acetylides with Weinreb amides followed by a Michael reaction of the extruded N-methoxy-N-methylamine after quenching with saturated NH₄Cl, provided β-enamino ketones in high yield and in a single geometrical isomeric form. It has been demonstrated that this method is applicable to a wide variety of such amides and to different acetylides.     

Effect of organo-modified clay on accelerated aging resistance of hydrogenated nitrile rubber nanocomposites and their life time prediction

Organically modified clay - reinforced hydrogenated nitrile rubber vulcanizate was subjected to accelerated heat aging to estimate its long-term thermo-oxidative stability and its useful lifetime was compared with that of the virgin polymer for the first time. Changes in technical properties such as tensile strength, modulus and elongation at break were studied as a function of time and temperature of aging. The infrared spectroscopic analysis of the degraded products revealed that under aerobic hot aging conditions, hydrogenated nitrile rubber (HNBR) compounds undergo cross-linking reactions that lead to embrittlement and ultimately failure. Incorporation of clay filler, however, resulted in significant improvement of the degradation profile of the nanocomposite at elevated temperatures. Loss of ductility during aging of the nanocomposite was also milder, relative to the unfilled polymer, indicating a restricted degradation by the clay filled rubber, thus prolonging the durability. From the scanning electron microscopy and atomic force microscopy studies, it was found that nanofillers protected the elastomer from surface rupture that took place on oxidation. Life prediction of both virgin elastomer and the nanocomposite indicated a three-fold increase in the effective service temperature range of the HNBR using 8 parts organically modified nanoclay.     

Zinc Oxide Nanoparticles: Green Synthesis and Biomedical Applications

Journal of Cluster Science - Nanoparticles refer to ultrafine particles with the particle size at nanoscale. When metals and metal oxides were synthesized at nanoscale, by their unique properties...     

Synthesis,Characterization, Properties,and Novel Applications of Fluorescent Nanodiamonds

In the last few years, fluorescent nanodiamonds (FNDs)  have been developed significantly as a new member in the nanocarbon family. The surface of FNDs is embedded with some crystallographic defects containing color centres which surmount the properties of other fluorochromes including up conversion and down conversion nanoparticles, quantum dots, nano tubes, fullerenes, organic dyes, silica etc. Some of the intriguing properties like inevitable photostability, inherent bio-compatibility, outstanding optical and robust mechanical properties, excellent magnetic field, and electric field sensing potentiality make FNDs appealing to some benevolent applications in numerous fields like bio-imaging, delivering drugs, fighting cancer, spin electronics, imaging of magnetic structure at nanoscale and as promising nanometric temperature sensor. The structure of FNDs has certain point defects on the surface among which negatively charged nitrogen vacancy centre (NV^?) is the most investigated color centre. The production of NV^? fluorescence nanodiamonds is the most challenging task as substitution of carbon atoms is required to create vacancies by causing irradiation from an electron beam which is followed by high temperature annealing. Thus, this review points out the relative advantages of FNDs containing negatively charged nitrogen vacancy centres produced from HPHT method or CVD method with those nanodiamonds produced through detonation process or pulsed laser ablation (PLA) method. The steps involved in the fabrication of FNDs are described along with the major challenges and struggles underwent during the process in this review. This review also summarizes the recent developments made in the functionalization and applications predominantly made in the field of biological science and it is understood that depending on the defect color centres they can exhibit different emitted wavelengths ranging from UV–visible to near infrared with broad or narrow bandwidths. This review also highlights some of the fluorescent NDs that emit stable and strong red or green photoluminescence from the defect centers of NV^? which are implanted in the crystal lattice. This critical and extensive review will be useful for the further progress in this futuristic field of FNDs.

     

Synthesis and conformational analysis of some cyanomethylene derivatives of piperidines

Five 4-dicyanomethylene derivatives 6–10, N-cyanoacetyl-cis-2,6-diphenylpiperidin-4-one 11 and 4-cyano(ethoxycarbonyl)-methylene-cis-2,6-bis(o-chlorophenyl)piperidine 12 were synthesised by condensing the appropriate piperidin-4-ones 13–17 with malononitrile/ethylcyanoacetate and their ¹H and ¹³C NMR spectra were recorded. The ¹H-¹H COSY spectrum for 6 and NOESY spectra for 8, 10, and 11 were also recorded. Based on coupling constants and the results obtained from NOESY spectra boat conformation for 10 and epimerised chair conformations for 8 and 9 have been proposed. Other derivatives adopt normal chair conformations. Theoretical calculations and the ¹H and ¹³C chemical shifts also support the above conformations. Mass spectra were also recorded for 6–12.