Ortho effects in organic molecules on electron impact. 12—Mechanism of the H2O loss from the molecular ion of 2-(phenylamino)benzoic acid

The mass spectrum of 2-(phenylamino)benzoic acid is characterized by the presence of the base peak at m/z 195, formed by the expulsion of H₂O from the molecular ion. A mechanism for the water loss, involving the ? COOH and ? NH functions followed by cyclization leading to the molecular ion of acridone, is proposed based on the study of the substituted derivatives and MIKE spectra.     

Cycloreversal reaction and ortho interactions in 2-aryl-4H-3, 1-benzoxazin-4-ones on electron impact

A cycloreversal reaction, leading to aroyl cations, is the major process in 2-aryl-4H-3,1-benzoxazin-4-ones under electron impact conditions. The ortho interaction of the methoxy and the nitro groups in the 2-phenyl moieties in these compounds present the most abundant ions at m/z 119 and 134, respectively, in their mass spectra as a result of the transfer of a hydrogen atom from the former and an oxygen atom from the latter to the imine nitrogen of the heterocycle. The ion structures and the mechanisms for the proposed fragmentations are based on high-resolution data, B/E and B²/E linked-scan spectra, collision-activated decomposition–B-/E linked-scan spectra and deuterium labelling.     

Synthesis of eupomatilone-6 and assignment of its absolute configuration

[Reaction: see text]. The Zn-mediated Barbier reaction of the biarylaldehyde 8 with crotyl bromide followed by hydroboration and oxidation provided the gamma-butyrolactones 4 and 5. The stereoselective installation of methyl group at C-3 by using LiHMDS and MeI completed the synthesis of racemic eupomatilone-6 (2) and its diastereomer 3. The spectroscopic data of 2 was in full agreement with reported spectra of natural product, thus confirming the revised relative configuration of eupomatilone-6. Similarly, an optically active (3R,4R,5S)-isomer of eupomatilone-6 (23) was prepared in which the aldol reaction with thiazolidinethione as a chiral auxiliary was employed as a key step. On the basis of the spectroscopic data and optical rotation values of 23, the absolute configuration of eupomatilone-6 was proposed.     

Unusual neutral and radical losses in 2′-substituted N-phenylanthranilic acids on electron impact

Unusual expulsions of [H₂O + CO₂] from the M⁺˙ of N-(o-carboxyphenyl)anthranilic acid, [H₂O + CH₂O] from the M⁺˙ of N-(o-methoxyphenyl)anthranilic acid and [H₂O + ˙NO₂] from the M⁺˙ of N-(o-nitrophenyl) anthranilic acid were observed under electron impact conditions. These processes are stepwise in the corresponding para-substituted N-phenylanthranilic acids. The proposed fragmentation pathways and their mechanisms are supported by B/E linked-scan spectra, collision-activated decomposition (CAD)–mass-analysed ion kinetic energy (MIKE) spectra, high-resolution data, deuterium labelling and chemical substitution.     

Second law analysis of the flow of two immiscible micropolar fluids between two porous beds

This work investigates the effect of entropy generation rate within the flow of two immiscible micropolar fluids in a horizontal channel bounded by two porous beds at the bottom and top. The flow is considered in four zones. Zone IV contains the flow of viscous fluid in the large porous bed at the bottom, zone I and zone II contain the free flow of two immiscible micropolar fluids, and zone III contains the flow of viscous fluid in the thin porous bed at the top. The flow is assumed to be governed by Eringen’s micropolar fluid flow equations in the free channel. Darcy’s law and Brinkman’s model are used for flow in porous zones, namely, zone IV and zone III, respectively. The closed form expressions for entropy generation number and Bejan number are derived in dimensionless formby using the expressions of velocity, microrotation and temperature. The effect of physical parameters like a couple stress parameter and micropolarity parameter on velocity, microrotation, temperature, entropy generation number and Bejan number are investigated.     

An expeditious one-step entry to the tetracyclic core of integrastatins

Herein we describe a one-step assembly of structurally complex small molecules representing the central skeleton of integrastatins by employing a simple pinacol transform.     

Pyrrolo-dC oligonucleotides bearing alkynyl side chains with terminal triple bonds: synthesis, base pairing and fluorescent dye conjugates prepared by the azide-alkyne "click" reaction

5-(Octa-1,7-diynyl)-2'-deoxyuridine was converted into the furano-dU derivative 7 by copper-catalyzed cyclization; the pyrolodC-derivative 3 was formed upon ammonolysis. The bicyclic nucleosides 3 and 7 as well as the corresponding non-cyclic precursors 4 and 6 all containing terminal C[triple bond]C bonds were conjugated with the non-fluorescent 3-azido-7-hydroxycoumarin 5 employing the copper(I)-catalyzed Huisgen-Sharpless-Meldal cycloaddition "click reaction". Strongly fluorescent 1H-1,2,3-triazole conjugates (30-33) are formed incorporating two fluorescent reporters-the pyrdC nucleoside and the coumarin moiety. Oligonucleotides incorporating 6-alkynyl and 6-alkyl 7H-pyrrolo[2,3-d]pyrimidin-2(3H)-one nucleosides (3 and 2f) have been prepared by solid-phase synthesis using the phosphoramidite building blocks 10 and 13 ; the pyrrolo-dC oligonucleotides are formed during ammonia treatment. The duplex stability of oligonucleotides containing 3 and related derivatives was studied. Oligonucleotides with terminal triple bonded nucleosides such as 3 are more stabilizing than those lacking a side chain with terminal unsaturation; open-chain derivatives (4) are even more efficient. The click reaction was also performed on oligonucleotides containing the pyrdC-derivative and the fluorescence properties of nucleosides, oligonucleotides and their coumarin conjugates were studied.     

Copper-catalyzed multicomponent green reaction approach: Synthesis of dihydropyrano [2,3-c] pyrazoles and evaluation of their anti-cancer activity

A facile, efficient, and simple one-pot multi-component protocol for the synthesis of pyrano[2,3-c] pyrazoles has been developed using a cheap and readily available copper catalyst under moderate reaction conditions. Target products are obtained from aromatic aldehyde via Knoevenagel condensation and Michael addition reactions. Functional group tolerance and reaction mechanisms have also been examined in this methodology. In addition, we have also evaluated the anti-cancer activity of the target products and we have attempted this method for practical utility purposes also.     

Supramolecular helical fluid columns from self-assembly of homomeric dipeptides

Herein, we demonstrate that with the widespread theme of residue patterning and stereochemical restraints of self-complimenting proteinogenic amino acids, a new and rich class of homomeric dipeptides exhibiting two-dimensional fluid aggregates with hierarchical ordering can be obtained. In particular, a simple way of achieving a class of functional dipeptides, wherein the first and the second residues chosen are L-/D-alanines and L-/D-leucines, has been accomplished. The supramolecules synthesized can be regarded as intermediates between polycatenars and taper-shaped amphiphiles because they possess two lipophilic segments interlinked by a peptide unit (spacer). Two pairs of enantiomers and their respective diastereomers derived from these amino acids are evidenced to self-organize into a helical columnar phase through hydrogen bonding by means of FTIR, UV/Vis, and chiroptical circular dichroism (CD) spectral analyses as well as by optical, calorimetric, electrical switching, and X-ray studies. The CD and X-ray studies have revealed that the form chirality (handedness) and the magnitude of out-of-plane fluctuations of the lattice planes of the fluid supramolecular columnar structures are solely directed by the stereochemistry encoded in the spacer. Of special significance, the less frequently found oblique helical columnar phase formed by a pair of enantiomers derived from L-/D-alanines, unlike those derived from other amino acids, exhibit ferroelectric behavior; the measured spontaneous polarization is as high as 440 nC cm(-2). Besides, all these supramolecules form stable organogels in ethanol and the CD and SEM studies on a representative gel suggest the presence of helical structures.