Stereoselective syntheses of unnatural steroidal C(20R) aldehydes by ionic hydrogenation of C-20 tertiary alcohols

Syntheses of three unnatural steroidal C(20R) aldehydes have been realised from 16-dehydropregnenolone acetate. The salient feature of the synthesis is the ionic hydrogenation of C-20 tertiary alcohols leading to the formation of the C(20R) unnatural isomer with complete stereoselectivity. Oxidative hydrolysis of the dithiane moiety furnished the C(20R) aldehydes.     

Microscopic examination of the 2,300-year-old excavated steel plowshare from northern India

In the present investigation, X-ray diffractometer, optical microscope, and scanning electron microscope were used to analyze the plowshare excavated from Ganwaria, UP, India. The main objective of the investigation was to determine the type of alloy, analysis of slag inclusion, and corrosion behavior. X-ray diffraction analysis showed the presence of α-iron. Microstructure consists of ferrite and pearlite grains; ferrite phase was soft in comparison to the pearlite. Optical micrograph at lower magnification revealed slag inclusions aligned in a specific direction, which indicates that the forge welding technique was used in the manufacturing of the object. The microstructural examination revealed that the object was manufactured from carbon steel. Entrapped slag inclusions were observed by scanning electron microscope and X-ray mapping, and slags were identified as SiO₂ and MgO. Goethite and lepidocrocite corrosion compound were found on the surface of the object.     

Synthesis of p-tert-Butylcalix[4] Arenes with Diester Bridge Spanning the 1,3-(Distal) Positions on the Lower Rim

Abstract

p-tert-Butylcalix[4]crown ether esters have been synthesized in good yield using two synthetic methods.     

Synthesis of New Macrocyclic Polyaza Compounds Containing 1-Methylpyrazole

New macrocyclic polyaza compoundscontaining the 1-methylpyrazole moiety are synthesizedin high yield by [2+2]dipodal condensation andreduction. The ring contracted structure of the Schiffbase has been elucidated by NMR. Two of thesemacrocycles form dinuclear complexes with copper andsilver. Macrocyclic Schiff base 5a extracts74.5% silver from aqueous to organic phase.     

Estimation of submarine groundwater discharge using radium mass-balance in Mumbai Harbour Bay,Mumbai, India

Journal of Radioanalytical and Nuclear Chemistry - The Mumbai Harbour Bay (MHB), Mumbai, India houses a large number of ports, industrial units and urban settlements thus the groundwater may be...     

C-3 β-lactam carbocation equivalents: versatile synthons for C-3 substituted β-lactams

An efficient and operationally simple strategy for the synthesis of differently C-3 monosubstituted (9) and disubstituted (10) monocyclic β-lactams is described. This involves reaction of β-lactam carbocation equivalents (8) with an active aromatic, aliphatic and heterocyclic substrates in the presence of a Lewis acid.     

Near-UV induced interstrand cross-links in anthraquinone-DNA duplexes

Anthraquinone (AQ) has been extensively used as a photosensitizer to study charge transfer in DNA. Near-UV photolysis of AQ induces electron abstraction in oligonucleotides leading to AQ radical anions and base radical cations. In general, this reaction is followed by the transport of base radical cations to sites of low oxidation potential, that is, GG, and conversion of G radical cations to DNA breaks. Here, we show that AQ also produces interstrand cross-links in DNA duplexes. About half of the cross-links collapse to single strands in hot piperidine treatment. The structure of stable interstrand cross-links was deduced by MS, NMR, and sequence substitution. The cross-links consist of a covalent link between the methyl group of T on one strand with either C6 or C7 of AQ on the other strand. The formation of interstrand cross-links decreased in O2 compared to deoxygenated solutions. In the presence of O2, the yield of breaks at GG doublets was 10-fold greater than that of cross-links for end tethered AQ, while cross-links exceeded breaks for centrally located AQ. The formation of stable cross-links can be explained by initial charge transfer from T to excited AQ, deprotonation of T radical cations, and condensation of the latter species with AQ radicals. These studies reveal a novel pathway of damage in the photolysis of AQ-DNA duplexes.     

(N-Benzyl-bis-N',N'-salicylidene)-cis-1,3,5-triaminocyclohexane copper(II): a novel catalyst for the aerobic oxidation of benzyl alcohol

Reaction of Cu(BF(4))(2).6H(2)O with the N(3)O(2) donor ligand H(2)L (where H(2)L = N-benzyl-N',N'-di-tert-butyl-disalicyl-triaminocyclohexane) results in the formation of a novel Cu(II)L complex, 1. X-Ray crystallography of it shows the Cu(II) centre coordinated by two phenolate oxygens and two imine nitrogens in a distorted square plane with an elongated bond to the amine nitrogen (2.512 A) in the axial position. EPR spectroscopy gives g values of g(1) = 2.277, g(2) = 2.100, g(3) = 2.025, and A(1) = 15.6 mT which are consistent with the distorted square pyramidal coordination environment determined from the X-ray structure. UV/visible and electrochemical analysis of shows that it undergoes two reversible processes assigned to the successive oxidation of the phenolate oxygens to phenoxyl radicals, the first at E((1/2)) = 0.89 V (DeltaE = 81 mV, vs. Ag/AgCl) and the second at E((1/2)) = 1.13V (DeltaE = 84 mV, vs. Ag/AgCl). Chemical oxidation results in the formation of a species, assigned as [1](+)(.) which is EPR silent due to antiferromagnetic coupling between the Cu(II) centre and the bound phenoxyl radical. The oxidised species catalyses the oxidation of benzyl alcohol to benzaldehyde.