Synthesis, characterization and antimicrobial activity of novel Schiff base tethered boronate esters of 1,2-O-isopropylidene-α-d-xylofuranose.

A series of twenty one Schiff bases based on boronate ester of 1,2-O-isopropylidene-α-d-xylofuranose scaffold were designed and synthesized by condensation of formyl or amino phenyl boronate esters with substituted anilines or 2-hydroxybenzaldehydes, respectively. All the imines are remarkably stable crystalline solids and were obtained in good yields. All the products were fully characterized by FT-IR, multinuclear NMR ((1)H, (13)C and (11)B) spectroscopy, and elemental analysis. Furthermore, the molecular structures of two of the Schiff bases were established by single crystal X-ray diffraction analysis. All the compounds have been screened for in vitro antimicrobial activity against various Gram-positive and Gram-negative bacterial and fungal strains. They exhibited moderate to good inhibitory activity against most of the tested organisms in comparison with standard drugs.

Sugar-boronate ester scaffold tethered pyridyl-imine palladium(II) complexes: synthesis and their in vitro anticancer evaluation.

A series of five palladium(ii) pyridyl-imine Schiff base complexes 5a-e containing boronate esters with protected sugar diols derived from d-xylose, l-sorbose and d-mannitol were designed and synthesized starting from pyridyl-imines generated in situ from 3-aminophenyl boronate ester of sugars 3a-e and 2-pyridinecarboxaldehyde, followed by the addition of Pd(cod)Cl2 in dichloromethane solvent. All the complexes are remarkably stable orange/yellow crystalline solids and were obtained in good yields. The complexes were fully characterized by FT-IR, multinuclear NMR ((1)H, (13)C and (11)B), UV-visible spectroscopy, and elemental analysis. The solid state structures of 3a and 5a were established by single crystal X-ray diffraction analysis. The complexes have been tested for their in vitro anticancer activities against human colon cancer (HT-29) and breast cancer (MDA-MB-231) cell lines. All the complexes have shown moderate to good cytotoxicity in both the cancer cell lines with IC50 values ranging from 4.27 to 34.76 µM. Strikingly, 5a displayed selective anticancer activity against both HT-29 and MDA-MB-231 cells with low IC50 values 6.71 and 8.58 µM respectively. Results also demonstrate that some of these complexes are highly potent against HT-29 cells as compared to the other cancer cell lines. In particular, 1,2:5,6-di-O-isopropylidene-d-mannitol complex 5d showed a two-fold higher toxicity against HT-29 cells in comparison with that of cisplatin. In addition, these complexes are less toxic to model non-tumorigenic human embryonic kidney cells (HEK-293T). Furthermore, the interaction of the complexes with calf thymus DNA (CT-DNA) was investigated using spectroscopy and viscosity measurements. It was found that they intercalate with DNA.

Design and synthesis of Tröger's base ditopic receptors: host-guest interactions, a combined theoretical and experimental study.

Two flexible Tröger's base ditopic receptors C4TB and C5TB incorporating monoaza crown ether were designed and synthesized for bisammonium ion complexation. A comprehensive study of host-guest interactions was established by (1)H NMR spectroscopy and DFT calculations. Bisammonium chloride (A1) with a shorter alkyl chain spacer showed the highest affinity for the receptors. M06-2X/cc-pVTZ calculations including the solvent effects on host-guest complexes were employed to explain and rationalize the experimental trends. The short N-H···O or N-H···N hydrogen-bond distances observed in the range of 1.71-1.98 Å indicate the existence of a strong charge assisted hydrogen bonding between the host and the guest. The unusual behaviour (higher binding constant) of A5 in (1)H NMR titration is traced to the conformational folding of the guest.

Iodine-catalyzed tandem synthesis of terminal acetals and glycol mono esters from olefins.

A new metal-free protocol is described for the synthesis of terminal acetals by tandem oxidative rearrangement of olefins using oxone as an oxidant in the presence of iodine. Moreover, a one-pot procedure for the preparation of glycol mono esters from olefins is also presented for the first time using the same reagent system.