@article { ISI:000227933800013, title = {Benzoyl transfer reactivities of racemic 2,4-Di-O-acyl-myo-inosityl 1,3,5-orthoesters in the solid state: molecular packing and intermolecular interactions correlate with the ease of the reaction}, journal = {Chemistry-A European Journal}, volume = {11}, number = {7}, year = {2005}, month = {MAR}, pages = {2103-2110}, publisher = {WILEY-V C H VERLAG GMBH}, type = {Article}, address = {PO BOX 10 11 61, D-69451 WEINHEIM, GERMANY}, abstract = {

Racemic 2,4-di-O-acyl-myoinosityl 1,3,5-orthoesters undergo transesterification catalyzed by sodium carbonate with varying ease of reaction in the solid state; reactions in solution and melt do not show such varied differences. An interesting crystal of a 1:1 molecular complex of highly reactive racemic 2,4-di-O-benzoyl-myo-inosityl 1,3,5-orthoformate and its orthoacetate analogue exhibited better reactivity than the latter component alone. Single-crystal X-ray structures of the reactants have been correlated with the observed differences in the acyl-transfer efficiencies in the solid state. Although each of the derivatives helically self-assembles around the crystallographic 2(1) axis linked through O-(HO)-O-... hydrogen bonding, the pre-organization of the reactive groups (C=O [El] and OH [Nu]), C-(HO)-O-... and the C=H(...)pi interactions are significantly more favourable for the reactive derivatives than the less reactive ones. Bond-length distributions also showed differences; the O-C bond of the axial benzoyl group, which gets cleaved during the reaction, is longer (1.345-1.361 angstrom) relative to the chemically equivalent O-C bond of the equatorial benzoyl group (1.316-1.344 angstrom) in the reactive derivatives. These bond-length differences are not significant in the less reactive derivatives. The overall molecular organization is different too; the strikingly discrete helices, which may be viewed as {\textquoteleft}{\textquoteleft}reaction tunnels{\textquoteright}{\textquoteright} and are held by interhelical interactions, are clearly evident in the reactive derivatives in comparison with the less reactive ones.

}, keywords = {hydrogen bonds, Inositol, solid-state reactions, structure elucidation, transesterification}, issn = {0947-6539}, doi = {10.1002/chem.200400851}, author = {Sarmah, M. P. and Gonnade, Rajesh G. and Shashidhar, M. S. and Bhadbhade, Mohan M.} } @article { ISI:000372848000021, title = {Disruption of native beta-turns: consequence of folding competition between native and orthanilic acid proline-based pseudo beta-turn}, journal = {European Journal of Organic Chemistry}, number = {7}, year = {2016}, month = {MAR}, pages = {1380-1388}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {

Five tetrapeptides comprising beta-turn-forming elements and a pseudo beta-turn (C9 H-bonding) based on an SAntPro (orthanilic acid - proline) motif were designed and synthesized. Their extensive conformational investigation by single-crystal X-ray crystallography, solution-state 2D NMR spectroscopic, and nOe-restrained MD simulation studies revealed the formation of C14 or C9 folding and disruption of the native beta-turn (C10 H-bonding) architecture. The striking difference between the psi(psi(2)) angle of {\textquoteleft}{\textquoteleft}i + 2{\textquoteright}{\textquoteright} residues of native beta-turn and designed peptides suggest that formation of the native beta-turn is not favored. The results suggest that other turn-forming motifs can dramatically modulate the stability of the native beta-turn structure.

}, keywords = {Conformation analysis, hydrogen bonds, Peptidomimetics, structure elucidation}, issn = {1434-193X}, doi = {10.1002/ejoc.201501558}, author = {Ingole, Tukaram S. and Vijayadas, Kuruppanthara N. and Chaitanya, K. N. and Kotmale, Amol S. and Gawade, Rupesh L. and Gonnade, Rajesh G. and Rajamohanan, P. R. and Sanjayan, Gangadhar J.} } @article {44654, title = {First total synthesis of the proposed structure of pandangolide 1}, journal = {European Journal of Organic Chemistry}, year = {2018}, month = {JUL}, pages = {3352-3364}, abstract = {

The first total synthesis of the proposed structure of pandangolide 1 is reported. The synthesis was carried out using both an organocatalytic approach and a chiral-pool approach. The required stereochemistry at C-3 and C-5 was installed by using an organocatalytic aldol reaction and a stereoselective ketone reduction. The construction of the 12-membered core was achieved by 2-methyl-6-nitrobenzoic anhydride-mediated Shiina lactonization. The structure of target molecule was confirmed unambiguously by single-crystal X-ray analysis, but the optical rotation and NMR spectroscopic data of the synthetic pandangolide 1 were found to be inconsistent with the natural product.

}, keywords = {lactones, Macrocycles, Natural products, structure elucidation, synthesis design, Total synthesis}, issn = {1434-193X}, doi = {10.1002/ejoc.201800675}, author = {Show, Krishanu and Gonnade, Rajesh G. and Kumar, Pradeep} }