排序方式: 共有95条查询结果,搜索用时 15 毫秒
1.
This work describes a rational approach for addressing the prototropy-related problems in heterocycle-based self-assembling systems by the use of degenerate prototropy. As a proof of principle, the utility of degenerate prototropy is demonstrated herein by developing heterocycle-based AADD-type self-assembling modules that exist as "single set of protameric pair (duplex)" in both solution and solid states. These self-assembling modules are quickly accessible in good yield by reacting 2-amino-5,5-disubstituted-1H-pyrimidine-4,6-diones, available in one step by the condensation of alpha,alpha-dialkyl malonates and free guanidine, with isocyanates. Evidence from NMR spectroscopy, ESI mass spectrometry, and single-crystal X-ray diffraction studies confirmed the formation of molecular duplexes. The effect of electronic repulsion in duplex formation is also investigated. Their ready synthetic accessibility, remarkably high propensity to crystal formation, and the novel property of degenerate prototropy would make these novel self-assembling molecules promising candidates for many proposed applications. 相似文献
2.
Bapurao B. Shingate Vandana S. Pore Rajesh G. Gonnade Mohan M. Bhadbhade 《Tetrahedron》2007,63(25):5622-5635
A stereoselective total synthesis of naturally occurring 20-epi cholanic acid derivatives has been realized, starting from readily available 16-dehydropregnenolone acetate. The key step of these syntheses involves an ionic hydrogenation of a C-20,22-ketene dithioacetal and deoxygenation of steroidal C-20 tert-alcohols, to set up the unnatural C(20R) configuration with 100% stereoselectivity. The unnatural C-22 aldehydes with C(20R) stereocenters thus obtained were elaborated to 20-epi cholanic acid derivatives. Two derivatives of 20-epi cholanic acid were synthesized and their structures have been confirmed by single crystal X-ray analysis. Catalytic hydrogenation of 16-dehydropregnenolone acetate and 16-dehydropregnenolone in ethanol affords C-5,C-16 tetrahydro products. Crystal structure analysis of one of these products revealed C-5α and C-17α configurations of the hydrogen atoms. 相似文献
3.
Gonnade RG Bhadbhade MM Shashidhar MS 《Chemical communications (Cambridge, England)》2004,(22):2530-2531
myo-Inositol hexabenzoate having meso configuration produces chiral polymorph (form I) when crystallized rapidly but yields achiral polymorph (form II) when allowed to crystallize slowly; in the mother liquor form I slowly but completely disappears to give form II. 相似文献
4.
Conformationally rigid aromatic amino acids as potential building blocks for abiotic foldamers 总被引:1,自引:0,他引:1
Ramesh VV Roy A Vijayadas KN Kendhale AM Prabhakaran P Gonnade R Puranik VG Sanjayan GJ 《Organic & biomolecular chemistry》2011,9(2):367-369
This communication describes the development of conformationally constrained unnatural aromatic amino acids, constructed on rigid backbone wherein the carboxyl and amino groups project in two dimensions (planes) on the aromatic framework. Such a feature offers the possibility of design and development of conformationally ordered synthetic oligomers with intriguing structural architectures distinct from those classically observed. Furthermore, such amino acids will have the potential to extend the conformational space available for foldamer design with diverse backbone conformation and structural architectures. 相似文献
5.
A new bis-andrographolide ether from Andrographis paniculata nees and evaluation of anti-HIV activity 总被引:3,自引:0,他引:3
Reddy VL Reddy SM Ravikanth V Krishnaiah P Goud TV Rao TP Ram TS Gonnade RG Bhadbhade M Venkateswarlu Y 《Natural product research》2005,19(3):223-230
Novel bis-andrographolide ether (1) and six known compounds andrographolide, 14-deoxy-11,12-didehydroandrographolide, andrograpanin, 14-deoxyandrographolide, (+/-)-5-hydroxy-7,8-dimethoxyflavanone, and 5-hydroxy-7,8-dimethoxyflavone have been isolated from the aerial parts of Andrographis paniculata and their structures were established by spectral data. All the isolates were tested for the anti-HIV and cytotoxic activity. 相似文献
6.
Chavan SP Sharma P Sivappa R Bhadbhade MM Gonnade RG Kalkote UR 《The Journal of organic chemistry》2003,68(17):6817-6819
Introduction of natural menthol as the chiral auxiliary in a gamma-Br-alpha,beta-unsaturated ester leads to enantioselective generation of three chiral centers in a single step on reaction with a glycine anion equivalent to provide L-CCG-I in 94% ee. 相似文献
7.
Patwa AN Gonnade RG Kumar VA Bhadbhade MM Ganesh KN 《The Journal of organic chemistry》2010,75(24):8705-8708
X-ray crystallographic studies of methylene linked Ferrocene-bis(thymine/uracil) conjugates Fc(T:T)(M) and Fc(U:U)(M) reveal base dependent 2-D supramolecular assemblies generated via wobble self-pairing for bis-thymine and reverse wobble self-pairing for bis-uracil conjugates, differing in architecture from the corresponding butylene spacer linked conjugates. 相似文献
8.
Sarmah MP Gonnade RG Shashidhar MS Bhadbhade MM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(7):2103-2110
Racemic 2,4-di-O-acyl-myo-inosityl 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-H...O hydrogen bonding, the pre-organization of the reactive groups (C=O [El] and OH [Nu]), C-H...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 A) relative to the chemically equivalent O-C bond of the equatorial benzoyl group (1.316-1.344 A) 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 "reaction tunnels" and are held by interhelical interactions, are clearly evident in the reactive derivatives in comparison with the less reactive ones. 相似文献
9.
[reaction: see text] The 1,4-dipole derived from isoquinoline and DMAD has been shown to react readily with N-tosylimines resulting in the diastereoselective synthesis of 2H-pyrimido[2,1-a]isoquinoline derivatives. 相似文献
10.
J?RG?FELDVOSSEmail author SALVATORE?SICILIANO THOMAS?WEIGEL 《Transformation Groups》2016,21(2):377-398
In this paper it is shown that the projective cover of the trivial irreducible module of a finite-dimensional solvable restricted Lie algebra is induced from the one dimensional trivial module of a maximal torus. As a consequence, the number of the isomorphism classes of irreducible modules with a fixed p-character for a finite-dimensional solvable restricted Lie algebra L is bounded above by p MT(L), where MT(L) denotes the maximal dimension of a torus in L. Finally, it is proved that in characteristic p > 3 the projective cover of the trivial irreducible L-module is induced from the one-dimensional trivial module of a torus of maximal dimension, only if L is solvable. 相似文献