S. S. Bari

Antioxidant activity and ultra-performance LC-electrospray ionization-quadrupole time-of-flight mass spectrometry for phenolics-based fingerprinting of Rose species: Rosa damascena, Rosa bourboniana and Rosa brunonii.

Roses are one of the most important groups of ornamental plants and their fruits and flowers are used in a wide variety of food, nutritional products and different traditional medicines. The antioxidant activity of methanolic extracts from fresh flowers of three rose species (Rosa damascena, Rosa bourboniana and Rosa brunonii) was evaluated by 1,1-diphenyl-2-picryl hydrazyl (DPPH) free-radical method. The ability to scavenge DPPH radical was measured by the discoloration of the solution. The methanolic extract from R. brunonii exhibited maximum free-radical-scavenging activity (64.5+/-0.38%) followed by R. bourboniana (51.8+/-0.46%) and R. damascena (43.6+/-0.25%) at 100 microg/ml. Simultaneously, ultra-performance liquid chromatography coupled with electrospray ionization-quadrupole time-of-flight mass spectrometry (UPLC-ESI-QTOF-MS) was used to study phenolic composition in the methanolic extracts from the fresh flowers of rose species. The phenolic constituents were further investigated by direct infusion-ESI-QTOF-MS/MS in negative ion mode. Characteristic Electrospray ionization tandem mass spectrometry (ESI-MS/MS) spectra with other diagnostic fragment ions generated by retro Diels-Alder (RDA) fragmentation pathways were recorded for the flavonoids. Distinct similarities were observed in the relative distribution of polyphenolic compounds among the three species. The dominance of quercetin, kaempferol and their glycosides was observed in all the three species.

Convenient Preparation of Benzylseleno‐ and Phenylselenoalkanoic Acids: Reagents for Synthesis of Organoselenium Compounds

Abstract An efficient and operationally simple route to benzylseleno‐ and phenylselenoalkanoic acids from ethyl benzyl/phenylselenoalkanoates is described. This involves preparation of ethyl benzyl/phenylselenoalkanoates as substrates by reaction of dibenzyl/diphenyl diselenide and sodium borohydride with ethyl chloroalkanoates in ethanol followed by basic hydrolysis and subsequent acidification.

A facile Lewis acid-promoted allylation of azetidin-2-ones

Abstract Exposure of 3α-chloro-3-phenylthioazetidin-2-ones and allyltrimethylsilane to a Lewis acid promotes a remarkably facile and stereoselective C-3 allylation to give 3α-allyl-3-phenylthioazetidin-2-ones 4 in excellent yield. These allylated azetidin-2-ones undergo smooth desulphurization with tri-n-butyltin hydride or Raney-nickel producing cis-3-allyl- and cis-3-propylazetidin-2-ones.

A new synthetic approach for novel C-3 substituted β-lactams

Abstract An effective route to novel C-3 substituted β-lactams is described. This involves reaction of a β-lactam carbocation equivalent with active aromatic nucleophiles in the presence of a Lewis acid. The stereospecificity of the formation of mono-substituted products may be rationalised on the basis of the SnCl 4 mediated intermediate complex A that reacts via an S N 2 mechanism.

An Unusual Lewis Acid Promoted Isomerization of trans-3-Halo-3-phenylthio-β-lactams

A method for C-3 epimerization of 3-halo-3-phenylthio-β-lactams, mediated by Lewis acids, is described. TiCl 4 promotes isomerization of trans-3-chloro-3-phenylthioazetidin-2-ones (2) to cis-3-chloro-3-phenylthioazetidin-2-ones (3). TiBr 4 promotes isomerization as well as substitution of chlorine with bromine affording isomeric cis- and trans-3-bromo-3-phenylthioazetidin-2-ones (5) and (6) respectively, while TiI 4 is ineffective.

Asymmetric Friedel–Crafts alkylation using chiral α-acyl-α-chloromethylsulphides

Abstract Lewis acid catalysed stereoselective Friedel–Crafts alkylation of aromatic compounds with α-(−)-menthyloxycarbonyl-α-(phenylthio)methyl chloride and α-(−)-8-phenylmenthyloxycarbonyl-α-(phenylthio)methyl chloride is described.

Stereoselective synthesis of novel monocyclic trans-3-halogenated-4-pyrazolyl-β-lactams: Potential synthons and promising biologically active agents

ABSTRACT Stereoselective synthesis of novel monocyclic trans-3-halogenated-4-pyrazolyl-β-lactams 5 is described. The reaction of ketene derived from α-bromo/chloroethanoic acids 4 using POCl3 and Et3N with pyrazolyl substituted imines 3a–d in refluxing toluene resulted exclusive formation of trans-β-lactams through [2 + 2] through cycloaddition reaction. The chemical structures of all the newly synthesized β-lactams were verified on the basis of spectroscopic techniques such as FTIR, 1H NMR, 13C NMR, and elemental analysis (CHN). The trans configuration of β-lactams 5 was assigned with respect to position of C3-H and C4-H. The novel β-lactams 5 are potential synthons for azetidines, aziridines, 3-unsubstituted azetidinones, 3-alkyl-halo-azetidinones, and promising biologically active agents. GRAPHICAL ABSTRACT

An efficient synthesis of spiro- β-lactams having sulfenyl, sulfinyl and sulfonyl moiety

AbstractAn efficient and a facile route to spiro- β-lactams is described. 3-allyl-3-methylthio- β-lactams, which are synthesized through a Lewis acid mediated C-3 alkylation of the trans-3-chloro-3-methylthio- β-lactams, undergo a facile intrasulfenyl cyclization reaction in the presence of halogens like bromine and iodine to give spiro β-lactams in good yield. These halospiro- β-lactams are then subjected to dehalogenation reaction using Raney-nickel. The resulting spiro- β-lactams are further transformed into their sulfinyl and sulfonyl derivatives by using m-chloroperbenzoic acid as an oxidant. Graphical AbstractA facile synthesis of novel sulfinyl and sulfonyl spiro-β-lactams through intramolecular cyclization of cis-3-allyl-3-methylthio-β-lactams is described.

Facile synthesis of novel α-methylene-pyrazole-carboxylate substituted imines and trans-β-lactams: Versatile synthons for diverse heterocyclic molecules

ABSTRACT A simple, facile, and high yielding stereoselective approach for the integration of α-methylene-pyrazole-carboxylates at the β-lactam nucleus is described. These monocyclic β-lactams have been synthesized by treatment of 2-phenoxy/benzylthio/phenylthio ethanoic acids or acetoxyacetyl chloride/phthalimidoacetyl chloride 5a–e with novel α-methylene-pyrazole-carboxylate imines 4a–c using Et3N and POCl3 in refluxing toluene. All of the newly synthesized α-methylene-pyrazole carboxylate imines 4a–c and their β-lactam derivatives 6a–h have been fully characterized by spectroscopic techniques such as FTIR, NMR (1H, 13C, and 13C DEPT-135), 2D-NMR (COSY and HSQC), and elemental analyses (CHN). The cycloaddition reaction was found to be highly stereoselective leading to the exclusive formation of trans-β-lactams 6a–h and trans configuration was assigned with respect to coupling constant values of C3-H and C4-H. The novel β-lactams 6a–h bearing α-methylene-pyrazole-carboxylate ring system will serve as useful synthons for highly functionalized acids, acetohydrazides/pyrazolones, alcohols, pyrazole carboxamides, peptides, and promising biologically active agents. GRAPHICAL ABSTRACT

Synthetic route for the novel pyrimidine-substituted alkanoate, acetohydrazide, and imines: Synthon for β-lactams

ABSTRACT A simple and efficient synthesis of novel pyrimidine-substituted alkanoate, acetohydrazide, and imines is described. The synthesis of novel ethyl 2-(2,6-dimethylpyrimidin-4-yloxy)acetate (EDMPyA) 2 was performed through SN2 O-alkylation of 2,6-dimethyl-4-hydroxypyrimidine 1 with ethyl haloacetate. The compound EDMPyA 2 was subjected to nucleophilic substitution reaction with hydrazine hydrate to afford novel 2-(2,6-dimethylpyrimidin-4-yloxy)acetohydrazide (DMPyAH) 3. This DMPyAH 3 upon condensation with differently substituted carbonyl compounds (aldehydes/ketones) furnished DMPyAH imines (DMPyAH-I) 4a–d. These imines can be used for the preparation of unique β-lactams. The structure elucidation of all the newly synthesized compounds was performed using spectroscopy (FT-IR, 1H and 13C NMR) and elemental analysis (C, H, N). GRAPHICAL ABSTRACT