Andivelu Ilangovan

A highly efficient green synthesis of 1, 8-dioxo-octahydroxanthenes

SmCl3 (20 mol%) has been used as an efficient catalyst for reaction between aromatic aldehydes and 5,5-dimethyl-1,3-cyclohexanedione at 120°C to give 1,8-dioxo-octahydroxanthene derivatives in high yield. The same reaction in water, at room temperature gave only the open chain analogue of 1,8-dioxo-octahydroxanthene. Use of eco-friendly green Lewis acid, readily available catalyst and easy isolation of the product makes this a convenient method for the synthesis of either of the products.

γ-Carbonyl quinones: radical strategy for the synthesis of evelynin and its analogues by C-H activation of quinones using cyclopropanols.

Cyclopropanols, on oxidative ring opening with AgNO3-K2S2O8 in DCM-H2O at room temperature and under open flask conditions, produced β-keto radicals which were successfully added to quinones to furnish γ-carbonyl quinones. This mild method has been applied to the synthesis of cytotoxic natural products, 4,6-dimethoxy-2,5-quinodihydrochalcone and evelynin.

Crystal structure, Hirshfeld surfaces and DFT computation of NLO active (2E)-2-(ethoxycarbonyl)-3-[(1-methoxy-1-oxo-3-phenylpropan-2-yl)amino] prop-2-enoic acid

Nonlinear optical (NLO) activity of the compound (2E)-2-(ethoxycarbonyl)-3-[(1-methoxy-1-oxo-3-phenylpropan-2-yl)amino] prop-2-enoic acid is investigated experimentally and theoretically using X-ray crystallography and quantum chemical calculations. The NLO activity is confirmed by both powder Second Harmonic Generation (SHG) experiment and first hyper polarizability calculation. The title compound displays 8 fold excess of SHG activity when compared with the standard compound KDP. The gas phase geometry optimization and vibrational frequencies calculations are performed using density functional theory (DFT) incorporated in B3LYP with 6-311G++(d,p) basis set. The title compound crystallizes in non-centrosymmetric space group P21. Moreover, the crystal structure is primarily stabilized through intramolecular N-H···O and O-H···O hydrogen bonds and intermolecular C-H···O and C-H···π interactions. These intermolecular interactions are analyzed and quantified using Hirshfeld surface analysis and PIXEL method. The detailed vibrational assignments are performed on the basis of the potential energy distributions (PED) of the vibrational modes.

1-Alkyl-(N,N-dimethylamino)pyridinium bromides: inhibitory effect on virulence factors of Candida albicans and on the growth of bacterial pathogens

A homologous series of 1-alkyl-(N,N-dimethylamino)pyridinium bromides, termed compounds 1-11, was synthesized and studied for antibacterial and antifungal activity. Of these, compound 8, containing a ten-carbon alkyl chain, showed maximum inhibition against all the tested bacterial strains. The highest antibacterial activity using a disc diffusion method was recorded against Mycobacterium smegmatis [zone of inhibition (ZOI): 45.75±0.25 mm], followed by Escherichia coli, Proteus mirabilis, Vibrio cholerae, Staphylococcus aureus and Salmonella typhi. In addition to antibacterial activity, compounds 3-11 displayed good inhibitory action against the human opportunistic yeast pathogens Cryptococcus neoformans and various Candida spp. The maximum ZOI was observed against Cryptococcus neoformans (51.5±0.5 mm) using compound 8, with ZOIs of 23.5±0.5, 32.0±0.0, 27.75±0.25 and 41.5±0.5 mm against Candida albicans, Candida glabrata, Candida tropicalis and Candida krusei, respectively. Furthermore, compound 8 caused inhibition of the candidal yeast-hyphae transition at a concentration of 0.29 µM and also inhibited the secretion of extracellular hydrolytic enzyme such as secreted aspartyl proteinase at subinhibitory concentrations. Compound 8 showed very little haemolytic activity at a concentration of 0.58 µM (1.315±0.75 %), with its highest haemolytic activity (47.806±2.32 %) observed at a concentration of 2.9 µM.

Synthesis, characterization and antimicrobial activity of 4-amino-1-alkyl pyridinium salts

A series of 4-amino-1-alkyl pyridinium bromide salts (1–10) were synthesized and antimicrobial activity was evaluated by disc diffusion as well as broth macro-dilution method. 4-Amino-1-hexadecylpyridinium bromide (10) which showed good inhibition against Candida albicans and C. glabrata also displayed good germ tube inhibition against C. albicans. Compound 8 shows very low haemolytic activity against human red blood cells. Compound 10 exhibits excellent antibacterial activity against Escherichia coli and Staphylococcus aureus. Inhibition of phospholipase enzyme secretion was also observed against compound 8 to find the possible mode of action.

2,2‐Bis(ethoxycarbonyl)vinyl (BECV) as a Versatile Amine Protecting Group for Selective Functional‐Group Transformations

A 2,2-Bis(ethoxycarbonyl) vinyl- (BECV) group was used for the selective protection of amines at room temperature in the presence of potentially interfering functional groups such as OH, SH, COOH as well as other NH(2) groups. Several functional group transformations such as esterification, O-alkylation, O-acylation, N-alkylation, N-acylation, S-alkylation can selectively be carried out in the presence of the BECV group. The selective deprotection of the BECV group was achieved in a short time using ethylenediamine at room temperature while several other functional groups such as benzoate, aliphatic esters, amides and ethers remain intact. The BECV group shows orthogonal stability against the common protecting groups such as Fmoc, Cbz and Boc.

Synthesis, DNA-binding study, and antioxidant activity of 14-aryl-14H-dibenzo(a,j)xanthene derivatives

A simple and efficient one-pot method for the synthesis of 14-aryl-14H-dibenzo[a,j]xanthene derivatives using Ni(ClO4)2·6H2O as a catalyst is described. DNA-binding properties of 14-aryl-14H-dibenzo[a,j]xanthene derivatives 1a, 1j, 1l, 1m, and 1n were investigated using calf thymus DNA by electronic absorption spectroscopy and fluorescence spectroscopy. Binding constant (Kb) with DNA was calculated from the absorption measurements. The spectral changes observed such as hypochromicity, red shift, and isosbestic point are consistent with the intercalation mode of binding of the chromophore into the stack DNA base pairs. Among the five, compound 1n with strong electron donating substituents on the phenyl ring shows better intercalative binding with DNA. Investigations of antioxidant properties show that the dibenzo[a,j]xanthene 1m with –OH group substitution has high radical scavenging properties against DPPH and ABTS+.

Invariant and variable intermolecular interactions in functionalized malonic acid half-esters: X-ray, Hirshfeld surface and PIXEL energy analyses

A series of functionalized malonic acid half-ester derivatives (parent compound MHE-1), with variations in functional groups at different positions on the aromatic ring, have been synthesized and crystal structures are determined at room temperature (296 K). The methyl (4-CH3, MHE-2) and chloro (4-Cl, MHE-3) derivatives are isomorphous with each other. The overall crystal packing of MHE-1–3 is similar. However, there are few differences observed between stacking of layers in these structures. Compounds with nitro (3-NO2, MHE-4) and ethyl ester (2-COOC2H5, MHE-5) substituents crystallize in different space groups and thus crystal packing is different when compared to MHE-1–3. In all the structures, intramolecular N–H⋯O and O–H⋯O hydrogen bonds generate a two fused S(6) ring motif. A detailed study is carried out to visualize intermolecular interactions observed in all five crystal structures (MHE-1–5) using Hirshfeld surface (HS) analysis with two dimensional fingerprint plots. The relative contribution of intermolecular H⋯H contacts in MHE-3 is substantially lower than that in MHE-1–2, though similar crystal packing arrangements of MHE-1–3 and MHE-2 and MHE-3 are isomorphous. From HS analysis it is clear that the observed H⋯H contact contribution (MHE-3) is a consequence of the presence of the chlorine substituent and growing contribution of Cl⋯H contacts. The relative contributions of other intermolecular contacts involving various atoms are comparable in MHE-1–3 structures. The intermolecular interaction energies are quantified using PIXEL for various molecular pairs extracted from respective crystal structures. Interestingly, there are some invariant and variable intermolecular contacts observed between different groups in all five structures.

K2S2O8-mediated metal-free direct C–H functionalization of quinones using arylboronic acids

Direct C–H functionalization of quinones with arylboronic acids is achieved using K2S2O8 as the sole and efficient green catalytic system. This method provides a straightforward and sustainable way to construct arylquinones via a radical pathway in moderate to good yields under metal-free conditions.

Simple access to 5-carboalkoxy-2,3-dihydro-4H-pyran-4-ones via domino acylative electrocyclization: the first three step total synthesis of the dihydronaphthopyran-4-one class of natural products

Intermolecular domino C-acylation/6π-oxaelectrocyclization between β-ketoesters and α,β-unsaturated acid chlorides took place readily in the presence of CaCl2 to afford a variety of polysubstituted 5-carboalkoxy-2,3-dihydro-4H-pyran-4-ones, in good yields. The products were successfully exploited as precursors, for a simple and efficient construction of a naphthalene fused pyran-4-one ring system. This intramolecular Friedel–Crafts acylative aromatization approach was useful for the synthesis of the phytogrowth inhibiting dihydronaphthopyranone class of natural products.