Microwave assisted amination of quinolone carboxylic acids: an expeditious synthesis of fluoroquinolone antibacterials

A facile amination of quinolone carboxylic acids to fluoroquinolone antibacterials under microwave irradiation is described

Epoxide-initiated cationic cyclization of azides: a novel method for the stereoselective construction of 5-hydroxymethyl azabicyclic compounds and application in the stereo- and enantioselective total synthesis of (+)- and (−)-indolizidine 167B and 209D

A novel and general method has been developed for the stereoselective construction of 5-hydroxymethyl azabicyclic ring skeletons based on epoxide-initiated cationic cyclization of azides. The key cyclization reaction was systematically studied with the model compound, 3-(1-oxa-spiro[2.4]hept-4-yl)propyl azide 3a, and EtAlCl2) was found to be an ideal choice as the catalyst. The generality of this transformation was further tested with different ring sizes, where six- and seven-membered epoxyazides 3b,c underwent smooth cyclization to give 5-hydroxymethyl azepine 4b and 5-hydroxymethyl azocine 4c, respectively, as a single detectable diastereomer. This novel methodology was elegantly applied in the stereoselective total synthesis of indolizidine alkaloids 167B and 209D. Further, the enantioselective total synthesis of natural and unnatural indolizidine alkaloids 167B and 209D was accomplished by using Sharpless asymmetric dihydroxylation as a key step

A convenient method for the N-formylation of secondary amines and anilines using ammonium formate

The N-formylation of secondary amines and anilines using ammonium formate as a formylating agent is described

Epoxide-initiated electrophilic cyclization of azides: a novel route for the stereoselective construction of azabicyclic ring systems and total synthesis of (±)-indolizidine 167B and 209D

A novel and general method for the stereoselective construction of 5-hydroxymethyl azabicyclic ring skeletons based on epoxide initiated electrophilic cyclization of azides has been developed and applied in the synthesis of (±)-indolizidine 167B and 209D with an overall yield of 16.5% and 17.8%, respectively. The efficiency of this methodology is further exemplified in the synthesis of azepine skeleton via tandem cation−olefin−azide cyclization

Ciprofloxacin-protected gold nanoparticles

The antibacterial drug ciprofloxacin (cfH) has been used to protect gold nanoparticles of two different mean diameters, 4 and 20 nm. The protection is complete with about 65 and 585 cfH molecules covering 4 and 15 nm particles, respectively. The nature of binding has been investigated by several analytical techniques. The nitrogen atom of the NH moiety of piperazine group binds on the gold surface, as revealed by voltammetric and spectroscopic studies. The cfH-adsorbed particles are stable in the dry state as well as at room temperature, and as a result, redispersion is possible. The rate of release of the drug molecule from the nanoparticles is more in the basic medium than in pure water, and the kinetics depend on the size of the particle; faster desorption is seen in smaller particles. The bound cfH is fluorescent, and this property could be used in biological investigations. This study shows that metal nanoparticles could be useful carriers for cfH and fluoroquinolone molecules. Most of the bound molecules could be released over an extended period of time

The Lindlar catalyst revitalized: a highly chemoselective method for the direct conversion of azides to N-(tert-butoxycarbonyl)amines

An exceptionally chemoselective method for the direct conversion of azides to N-(tert-butoxycarbonyl)-protected amines under catalytic transfer-hydrogenation conditions, using the Lindlar catalyst, is reported. The extremely labile functional groups such as N-Cbz, benzyl ester are shown to be inert under the reaction conditions. The present method allows us to synthesize orthogonally protected (N-Cbz & N-Boc) 1,2-diamino systems, which will be immensely useful in organic synthesis

Fluorescent nanobubbles

Degradation of halocarbons using silver and gold nanoparticles has been utitlised for the synthesis of empty nanoshells of nanobubbles starting from coreshell particles. The studies conducted were mainly on zirconia and silica nanoshells. Removal of the metal core was followed by UV-visible spectroscopy. The properties of nanoshells were further modified by incorporating molecules namely ciprofloxacin and aniline inside shell. The new materials obtained were characterized using UV-visible spectroscopy, emission spectroscopy and transmission electron microscopy. Aniline@SiO2 was found to have pH sensing property with complete reversibility. When confined inside the silica shell, aniline shows an additional red shifted peak apart from the usual fluorescence peak. This additional peak is attributed to the emission from excimers of aniline