Letters in Organic Chemistry - Volume 2, Issue 6, 2005

Recent progress in molecular biology and genetics has invigorated interest in modified nucleic acids both for fundamental studies and for practical applications. Herein, recent advances in design of modified non- Watson-Crick base pairs are highlighted. Examples of altered hydrogen-bonding patterns, size-expanded bases, and base pairing dependent on metal chelation and hydrophobic interactions are discussed.

3-Alkyl(aryl)-2,3-dihydro-1H-2-imidazolone derivatives as unexpected product of the reaction between ethyl 3-alkyl(aryl)amino-2-oximinobutanoate and methyl orthoformate is described. These imidazolones are generated by an intramolecular attack and a migration of N3-oxide oxygen from the imidazole N3-oxide intermediates. This proposed mechanism is supported by the results of theoretical studies (DFT).

A type of novel larger imidazolium cyclophanes have been designed and synthesized by ingeniously employing intermediates with spacers. The tandem-MS has been employed to certify that the cyclophanes unarguably have symmetrical structures like calix[8]arene.

Addition of γ-silyloxyallylstannanes to imines in the presence of trimethylsilyl triflate was studied. Allylation of α-imino ester with (Z)-allylstannane proceeded to give anti-adduct as a major product, which was transformed into N,O,O-triacetyl erythro-sphingposine via appropriate functional group transformations.

The allylic alcohol of the side-chain of larixol was converted into an exo 1,3-diene through trifluoroacetylation followed by palladium-catalyzed elimination; this allowed the introduction of a benzoquinone pharmacophore on this labdane platform in 'one-pot' from allylic trifluoroacetates.

Synthesis of novel fluorinated tetraphenylethene systems 5a-c was carried out and resulting new materials were investigated for their mesomorphic properties. New materials (5a-c) were prepared by the esterification of 3 with either 4-trifluoromethoxybenzoic acid (5a), 3,4,5-trifluorobenzoic acid (5b), or 4- trifluoromethylbenzoic acid (5c). All compounds (5a-c) were fully characterized while stereochemical fea Read More

A very efficient strategy for the chemical synthesis of the sialyl Lewis X tetrasaccharide is reported. Starting from four simple monosaccharide building blocks, sialyl Lewis X was obtained in seven steps. By using similar strategy, sialyl LacNAc and sulfated sialyl LacNAc trisaccharides were also synthesized.

Asymmetric Nozaki-Hiyama allylations using a proline derived amino alcohol as a chiral ligand showed good enantioselectivity (er up to 90:10). The results suggest that efficient catalysts for this type of chromium-mediated reactions may be designed using multidentate ligands based on sp3 hybridized backbones.

Two synthetic approaches of simpler jaspamide derivatives were investigated. The ring closure step was attempted either by RCM or by macrolactonisation. 14-Membered ring derivatives 15-16 were prepared by final macrolactonisation using Yamaguchi reagent.

A microwave-assisted, environment friendly, high yielding, time saving synthesis of medicinally important 3-substituted isocoumarins was carried out in a single step by the direct condensation of homophthalic acid with aryol and acyl chlorides under the solvent-free conditions without any solid support. The synthesized isocoumarins were structurally characterized by microanalysis, 1H-NMR, EI, IR and UV.

Synthesis of amino acid carbamate derivatives of quercetin from partly protected quercetin and amino acid esters utilizing triphosgene as an auxiliary reagent was studied. A series of quercetin derivatives were obtained regioselectively by reaction with amino acid ester isocyanates under mild conditions and in high yields.

Synthesis of 2,3,2',3'-tetrahydro-1H,1'H-[2,2']biindenyl 2 from the dimerization reaction of indene with lithium naphthalenide was carried out and we here report its single crystal X-ray structure. Synthesis and characterization of compounds 3-8 have also been carried out successfully. The stability of biindenyl and its stereochemistry at position 2 and 2' was investigated using density functional theory.

Alcohols are conveniently converted to their corresponding carbonyl compounds with CrO3 supported on NaHSO4.H2O in solution and under solvent free conditions.

A simple and facile synthesis of (+)-gloeosporone was developed using chirons that were available by lipase catalyzed acylation and chemical resolution.

Commercially available tetraalkylphosphonium ionic liquids are effective as solvents in the mild nitration of various arenes and offer some advantages over the more common N, N-dialkylimidazolium ionic liquids.

Photocleavage of lysozyme and bovine serum albumin (BSA) by L-phenylalanine-1(1- pyrene)methylamide (PMA-L-Phe) is reported here. The chiral probe, PMA-L-Phe, has a positively charged side chain, while the previous probes carried a free carboxyl group. The yield of lysozyme cleavage by PMA-LPhe is increased to 57% when compared to the previous probes, while the yield of BSA cleavage is reduced to <5%. Sequencing s Read More

Oxidation of aromatic alcohols to corresponding aldehydes and ketones have been carried out using molecular oxygen and FeCl3 supported on kieselguhr as catalyst in good yields.

Hydroxyapatite doped with ZnCl2, CuCl2, NiCl2 and CoCl2 efficiently catalyses the three components Biginelli reaction between an aldehyde, ethyl acetoacetate and urea in refluxing toluene to afford the corresponding dihydropyrimidinones in high yields.

The Michael addition of ketone-derived enamines to γ-fluoro-α-nitroalkenes provides in moderate to good isolated yields the corresponding β-fluoroalkyl γ-nitroketones, which can be reduced to β-fluoroalkyl γ- nitroalcohols.