Synthesis of the ‘southern’ tripeptide of Cyclomarins A and C having novel anti-tuberculocidal mode of action

The synthesis of the ‘southern’ tripeptide of Cyclomarins A and C has been described which includes two unusual amino acids. The unusual amino acids have been synthesized and coupled with l-alanine to obtain the tripeptide.     

Enhanced non-metallic behavior on the verge of magnetic instability in Fe2V1−xNbxAl Heusler alloys

Structural, magnetic and transport behavior of Nb substituted Fe₂VAl alloys have been investigated in the present work. From the detailed analysis of these data it is observed that Nb content promotes a lattice expansion in L2₁ super-structure of Fe₂VAl. Magnetization data suggest that un-doped Fe₂VAl exhibits cluster glass behavior with a bimodal distribution of superparamagnetic clusters at lower temperatures, developed possibly due to the cluster size distribution. However, in Nb-substituted alloys, cluster size reduces and cluster density increases, which further reduces coupling between the clusters, resulting in a state of increased magnetic disorder up to a plausible 20% substitution. Concurrently resistivity increases at lower temperatures and shows a deviation from semiconductor like transport, which can be explained in terms of increasing spin dependent scattering and decreasing inter cluster interaction due to iso-electronic-but-larger-sized Nb substitution at V site. Present experimental results corroborate well with the theoretical predictions made in the literature.     

The synthesis of (1S,8aS)-1-hydroxyindolizidine using a stereoselective Grignard addition to an N-benzyl-3-deoxy sugar imine derived from D-Glucose

A highly stereoselective approach to 1-hydroxyindolizidine is described using a Grignard reaction on N-benzyl imine derived from 3-deoxy-1,2-O-isopropylidine-α-d-xylo-pentodialdofuranose and reductive cyclization as key steps.     

Total synthesis of (−)-seimatopolide A

The total synthesis of (?)-seimatopolide A is described in a linear fashion with high yielding steps. The key reactions include Lu’s isomerization, Sharpless asymmetric dihydroxylation and Kita’s macrolactonization.     

Bromoacetone: A New Protective Group For 1,2-Diols Cleavable with Zinc

Bromoacetone has been utilized for the first time as an excellent protective group for 1,2-diols that can be cleaved under neutral conditions viz., refluxing in Zn - MeOH.     

Novel Chemosensor for the Visual Detection of Copper(II) in Aqueous Solution at the ppm Level

A new water-soluble, multisite-coordinating ligand LH(7) was prepared by the condensation of tris(hydroxymethyl)aminomethane with 2,6-diformyl-p-cresol. LH(7) is a selective chemosensor for Cu(2+), under physiological conditions, with visual detection limits of 20 ppm (ambient light conditions) and 4 ppm (UV light conditions). LH(7) can also be used in biological cell lines for the detection of Cu(2+).     

Catalysis by zeolite leading to the construction of thiazole ring: an improved synthesis of 4-alkynyl substituted thiazoles

Zeolite H-beta facilitated the reaction of α-chloro acetyl chloride with 1,2-bis-trimethyl silyl acetylene to give 1-chloro-4-(trimethylsilyl)but-3-yn-2-one which on treatment with thioacetamide afforded 2-methyl-4-[(trimethylsilyl)ethynyl]thiazole. l-Proline on the other hand facilitated the coupling reaction of 2-methyl-4-[(trimethylsilyl)ethynyl]thiazole with (hetero)aryl halides (modified Sonogashira reaction) under Pd-Cu catalysis in the presence of aqueous K₂CO₃ affording an improved method for the synthesis of corresponding 4-alkynyl substituted thiazole derivatives.     

Hydrophobic Interactions in Donor-Disulphide-Acceptor (DSSA) Probes Looking Beyond Fluorescence Resonance Energy Transfer Theory

Donor –linker –acceptor (DSSA) is a concept in fluorescence chemistry with acceptor being a fluorescent compound (FRET) or quencher. The DSSA probes used to measure thiol levels in vitro and in vivo. The reduction potential of these dyes are in the range of ?0.60 V, much lower than the best thiol reductant reported in literature, the DTT (?0.33 V). DSSA disulphide having an unusually low reduction potential compared to the typical thiol reductants is a puzzle. Secondly, DSSA probes have a cyclized rhodamine ring as acceptor which does not have any spectral overlap with fluorescein, but quenches its absorbance and fluorescence. To understand the structural features of DSSA probes, we have synthesized DSSANa and DSSAOr. The calculated reduction potential of these dyes suggest that DSSA probes have an alternate mechanism from the FRET based quenching, namely hydrophobic interaction or dye to dye quenching. The standard reduction potential change with increasing complexity and steric hindrance of the molecule is small, suggesting that ultra- low Eo’ has no contribution from the disulphide linker and is based on structural interactions between fluorescein and cyclized rhodamine. Our results help to understand the DSSA probe quenching mechanism and provide ways to design fluorescent probes.     

N-heterocyclic carbene-mediated hydroacylation-Sonogashira/Heck/Suzuki coupling in a single pot: a new cascade reaction

A dually NHC-catalyzed reaction cascade comprising an initial hydroacylation of an activated ketone and subsequent Sonogashira/Heck/Suzuki coupling in the same pot is reported. The reaction mechanism and scope of the methodology is presented.