Reshmi Mukherjee

Multiple hydrogen bonds and tautomerism in naphthyridine derivatives

The behaviour of three 2,7-disubstituted 1,8-naphthyridines able to exhibit tautomerism has been studied by NMR in solution and in two cases in the solid state. The three derivatives studied are 2,7-dihydroxy- (1), 2-acetamido-7-amino- (3) and 2,7-diacetamido-1,8-naphthyridine (4). To explore the problem of secondary interactions, a series of complexes, with up to four simultaneous hydrogen bonds, where the monomers are generated using pyridine and 4-pyridone as building blocks, have been theoretically studied. The calculated interaction energies have been correlated with the number of hydrogen bonds and with attractive and repulsive secondary interactions. Further analysis of the electron density and orbital interactions shows that the secondary interactions, both attractive and repulsive, have a purely electrostatic origin. The X-ray structure of compounds 3 and 4 have been determined. In the solid state these compounds exist in the “diamino” tautomers with the N–H proton of the amido groups pointing towards the naphthyridine nitrogen. DFT and GIAO calculations have been essential to disentangle the problem of the structure of these compounds.

Recognition of insoluble tartaric acid in chloroform

Abstract Simple receptors for the recognition and solubilisation of insoluble tartaric acid in chloroform were designed and synthesised for the first time. Receptors 2 and 3 were successful in solubilising tartaric acid into chloroform forming a 1:1 complex, and were also found to be useful as fluorescent probes for the detection of this substrate.

Simple and Efficient Synthesis of 2,7-Difunctionalized-1,8-Naphthyridines

The syntheses in good yields of some new difunctionalized 1,8-naphthyridines 4, 6, 8 and 9 and a novel triethylene glycol ether-linked dinaphthyridine, 10a, along with the mononaphthyridine-linked ether alcohol 10b are described. An improved and milder method for the synthesis of 2,7-diamino-1,8-naphthyridine (14) is also reported.

Molecular recognition of xanthine alkaloids: First synthetic receptors for theobromine and a series of new receptors for caffeine

Synthetic receptors (H3, H4, H5 and H6) are designed and synthesised for the first time for theobromine, a xanthine alkaloid used as a diuretic. The synthesis of the receptor H6 is achieved by Co(PPh3)3Cl-mediated homocoupling of 3-(ethoxycarbonyl)benzyl bromide 12 under mild conditions. New caffeine receptors (H7, H8 and H9) are designed and synthesised. The binding results of theobromine and caffeine (both by NMR and UV studies) are reported.

Novel Motif of Hydrogen Bonds in the Water-assisted Supramolecular Self-assembly of 2-acetylamino-6-methylpyridine-N-oxide and Hetero-assembly of 1:1 Co-crystal of o-Phenylenediamine with Catechol

Abstract Water assisted supramolecular structures of 2-acetylamino-6-methylpyridine-1-oxide (1) and 1:1 complex of o-phenylenediamine with catechol (2) were determined. The crystal structure of 2-acetylamino-6-methylpyridine-1-oxide. H2O (1), triclinic, a = 7.1276 (6), b = 7.8860 (6), c = 8.9938 (7) Å, α = 100. 143 (2), β = 91.493 (2), γ = 110.972 (1)°, V =462.47 (6) Å3, Z = 2, D calc = 1.323 mg.m−3(293°K) reveals a novel centrosymmetric supramolecular assembly that is sustained by water molecules linking the dimers of pyridine-1-oxide through C—H…O, N—H…O, N+—O− … H hydrogen bonds. The pyridine rings of the dimers are stacked at 3.473 Å apart, involving π- stacking interactions. Complex (2), C6H8N2.—C6 H6O2. 1/2H2O crystallises in the monoclinic space group P2/c: a = 9.0498(2), b = 5.2275(1), c = 25.0771(2) A, β = 97.71°, V= 1175.62(4) Å3, Z = 4. Refinement led to a final conventional R value of 0.041 for 2016 reflections. In these crystals (2), the water molecules lie on the twofold axis and they are linked to the pyrocatechol molecules through an O—H…O hydrogen bond.

Interaction of adenine with synthetic receptors: a theoretical study

The interaction of adenine with synthetic macrocyclic receptors has been modelled using, as simplified molecular systems, the monoamide derivatives of pyridine and 1,8-naphthyridine. DFT methods (B3LYP/6-31+G**) have been used to characterise the complexes stabilised by multiple hydrogen bonds. The theoretical results indicate that while the synthetic receptors with pyridines can interact simultaneously forming pseudo-Watson–Crick and pseudo-Hoogsten complexes with adenine, in the case of the 1,8-naphthyridines only one of the complexes is possible. The energetic results that favour the pyridine receptors are in agreement with the experimental binding constants.

o‐Phenylenediamine Pyrocatechol Hemihydrate Complex

A well defined supramolecular structure, C 6 H 8 N 2 .-C 6 H 6 O 2 .0.5H 2 O, is generated by molecular recognition between pyrocatechol and o-phenylenediamine in the presence of water. They spontaneously self assemble through a unique network of hydrogen bonds around a twofold axis.