Stereoselective first total synthesis of (R)-rugulactone

A simple and highly efficient stereoselective synthetic route has been developed for the synthesis of (R)-rugulactone, a 6-arylalkyl-5,6-dihydro-2H-pyran-2-one, from readily available substrates such as 1,3-propanediol and 3-phenyl-1-propanal employing Keck’s asymmetric allylation and cross metathesis as key steps.     

Stereoselective Total Synthesis of (3S,5S)‐1,7‐Bis(4‐hydroxyphenyl)heptane‐3,5‐diol, (3S,5S)‐Alpinikatin,and Its Diastereoisomers

Stereoselective synthesis of the diarylheptanoids, (3S,5S)‐1,7‐bis(4‐hydroxyphenyl)heptane‐3,5‐diol ( 1 ), (3S,5S)‐alpinikatin ( 3 ), and their diastereoisomers ( 2 and 4 , resp.), was achieved from readily available 4‐hydroxybenzaldehyde. The synthetic sequences involve Browns's allylation and Et₂Zn mediated diastereoselective alkynylation reaction as key steps.     

Elastic Behaviour of Some Substituted Nickel ferrites

The longitudinal and shcar wave velocities of some substituted nickel ferrites Ni_1.05Sn_0.05Fe_1.9-x (Cr or Al)_xO₄ were determined at room temperature by the pulse transmission technique. The elastic moduli have been corrected to theoretical density. A linear relationship between Debye temperature and average sound velocity has also been observed.     

Structural and morphological studies on Mn substituted ZnO nanometer‐sized crystals

Mn substituted ZnO nanocrystals synthesized by a co‐precipitation method. X‐ray diffraction (XRD) studies confirms the presence of wurtzite (hexagonal) crystal structure similar to un doped ZnO, suggesting that doped Mn ions go at the regular Zn sites. The lattice parameters a and c are increasing with increasing Mn content. The unit cell volume increases with increasing Mn concentration, indicating the homogeneous substitution of Mn²⁺ for the Zn²⁺. The lattice distortion parameter (ε_v) is evaluated from XRD data and found that it enhances as Mn content increases. Transmission electron microscopy photographs show that the size of the ZnO crystals is in the range of 20‐50 nm. The SAED pattern confirms the hexagonal and crystalline nature of the samples which are in agreement with X‐ray analysis. The chemical groups of the samples have been identified by FTIR studies (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Domino Knoevenagel-hetero-Diels-Alder reactions: a stereoselective synthesis of sugar-annulated furo[3,2-b] pyrano[4,3-d]pyran derivatives

The O-propargyl derivative of a sugar aldehyde derived from d-glucose undergoes smooth intramolecular domino Knoevenagel-hetero-Diels-Alder reactions with 1,3-diketones in the presence of CuI/Et₃N system in refluxing methanol to afford a novel class of carbohydrate analogues, furopyranopyrans in good yields. 1-Aryl-pyrazol-5-ones also undergo smooth coupling with O-propargyl tethered sugar aldehyde under similar conditions to furnish pyrazole-annulated furopyranopyrans. The stereochemistry of the products was assigned by various NMR experiments.     

Three‐Residue Turn in β‐Peptides Nucleated by a 12/10 Helix

A new three‐residue turn in β peptides nucleated by a 12/10‐mixed helix is presented. In this design, β peptides were derived from the 1:1 alternation of C‐linked carbo‐β‐amino acid ester [BocNH‐(R)‐β‐Caa_(r)‐OMe] (Boc=tert‐butyloxycarbonyl), which consisted of a D ‐ribo furanoside side chain, and β‐hGly residues. The hexapeptide with (R)‐β‐Caa_(r) at the N terminus showed the ‘turn’ stabilized by a 14‐membered NH(4) ??? CO(6) hydrogen bond at the C terminus nucleated by a robust 12/10‐mixed helix, thus providing a ‘helix‐turn’ (HT) motif. The turn and the helix were additionally stabilized by intraresidue electrostatic interaction between the furan oxygen in the carbohydrate side chain and NH in the backbone. However, the hexapeptide with a β‐hGly residue at the N terminus demonstrated the presence of a 10/12 helix through its entire length, which again showed the intraresidue interaction between NH and furan oxygen. The intraresidue NH ??? O? Me electrostatic interactions observed in the monomer, however, were absent in the peptides.     

Photon-driven nanomechanical cyclic motion

Microcantilevers modified by a monolayer of azobenzene molecules bend up and down periodically, switched by a 365 nm UV light, as a result of the conversion of the two configurations of azobenzene molecules in the monolayer.     

Synthesis, utility, and X-ray crystal structure of novel complexes of baccatin III with imidazole and 2-propanol

Baccatin III forms crystalline complexes 4 and 5 with imidazole and 2-propanol, respectively. These compounds are useful in the purification of baccatin III from mixtures of taxanes derived from plant-cell fermentation.