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21.
22.
Bonner BE Buchanan JA Clement JM Corcoran MD Krishna NM Kruk JW Miettinen HE Moss RM Mutchler GS Nessi-Tedaldi F Nessi M Phillips GC Roberts JB Stevenson PM Tonse SR Birman A Chung SU Etkin A Fernow RC Kirk H Protopopescu SD Willutzki H Hallman T Madansky L Bar-Yam Z Dowd J Kern W King E Mayes BW Pinsky LS 《Physical review D: Particles and fields》1990,41(1):13-16
23.
Bonner BE Buchanan JA Clement JM Corcoran MD Krishna NM Kruk JW Lincoln DW Miettinen HE Mutchler GS Nessi-Tedaldi F Nessi M Phillips GC Roberts JB Stevenson PM Tonse SR White JL Chung SU Etkin A Fernow RC Protopopescu SD Willutzki H Hallman T Madansky L Pinsky LS 《Physical review letters》1989,62(14):1591-1594
24.
Krishna B. Pandeya Trilochan S. Waraich Ramesh C. Gaur Rajendra P. Singh 《Transition Metal Chemistry》1982,7(3):146-148
Summary Tris-chelates of chromium(III) have been synthesised with five new dithiocarbamates, [RR'NCS2]–, where R=PhCH2 and R/t'=H, PhCH2, Me, Et and i-Pr. Magnetic moments together with electronic, i.r. and e.s.r spectra of the complexes have been described. Various ligand-field parameters have been evaluated and discussed. 相似文献
25.
Reddy PN Srikanth R Swamy NS Srinivas R Sharma GV Nagendar P Krishna PR 《Journal of mass spectrometry : JMS》2005,40(11):1429-1438
Positive and negative ion electrospray ionization (ESI) tandem mass spectral study of a new series of hybrid peptides, viz, BocN-alpha,beta-peptides and BocN-beta,alpha-peptides, synthesized from C-linked carbo-beta3-amino acids [Caa (S)] and L-Ala has been carried out. The alpha,beta-peptides have been differentiated from beta,alpha-peptides by the collision-induced dissociation (CID) of [M + H]+ and [M - H]- ions in positive and negative ion ESI-MS respectively. The fragment ion [M + H - C(CH3)3 + H]+ formed from [M + H]+ ions by the loss of 2-methyl-prop-2-ene in alpha,beta-peptides with L-Ala at the N-terminus is insignificant or totally absent for beta,alpha-peptides which have the Caa (S) at N-terminus. The fragment ion [M - H-C(CH3)3OH - HNCO]- formed from [M - H]- of beta,alpha-peptide acids is totally absent for alpha,beta-peptide acids. This has been attributed to the absence of the beta-methylene group in alpha,beta-peptides, and the participation of the beta-methylene group in the loss of HNCO in beta,alpha-peptide acids is confirmed by the deuteration experiments. The CID of [M + H-Boc + H]+ ions of these peptides also produce characteristic fragmentation. In the CID spectra of alpha,beta-peptides, the b(n)+ ions and the resulting y(n)+ ions occur at a mass difference of 243 and 71 Da corresponding to the successive losses of Caa and L-Ala, whereas a mass difference of 71 and 243 Da is observed for beta,alpha-peptides. In contrast to the CID of protonated peptides, the CID of [M - H]- ions of the alpha,beta- and beta,alpha-peptide acids do not give b(n)- ions and show abundant z(n) (-) ions. Further, a pair of diastereomeric dipeptide esters and acids have been distinguished by the CID of [M + H]+ ions. The loss of 2-methyl-prop-2-ene is more pronounced for Boc-NH-Caa(R)-D-Ala-OCH3 (21) and Boc-NH-Caa(R)-D-Ala-OH (23) with Caa (R) at the N-terminus, whereas it is totally absent for Boc-NH-Caa (S)-D-Ala-OCH3 (22) and Boc-NH-Caa(S)-D-Ala-OH (24) peptides, which have Caa (S) at the N-terminus. Thus, on the basis of our previous and present studies, we propose that the CID of [M + H]+ ions provides a simple and useful method for distinguishing the configuration of Caa (S or R) at the N-terminus of BocN-carbo beta,alpha- and beta,beta-dipeptides. 相似文献
26.
Krishna Kumar Gollapelli Vaibhav B. Patil Allam Vinaykumar Rambabu Chegondi 《Chemical science》2021,12(4):1544
A Rh(i)-catalyzed highly stereoselective desymmetrization of 2-alkynylbenzaldehyde-tethered cyclohexadienones triggered by intramolecular Huisgen-type [3 + 2] cycloaddition has been developed. This method enables convergent construction of complex epoxy-bridged polycyclic ring systems with five contiguous stereocenters with excellent exo-selectivity and broad substrate scope. The highly atom-economical process involves 6-endo-dig cyclization of carbonyl oxygen onto an activated alkyne resulting in a highly reactive metal–benzopyrylium intermediate, which readily undergoes intramolecular [3 + 2] annulation/hydration. Asymmetric induction is also achieved for the first time in Rh(i)-catalyzed 1,3-dipolar cycloaddition using an easily accessible chiral diene as the ligand.A Rh(i)-catalyzed highly stereoselective desymmetrization of 2-alkynylbenzaldehyde-tethered cyclohexadienones triggered by intramolecular Huisgen-type [3 + 2] cycloaddition has been developed. 相似文献
27.
We report here a methodology for the construction of a conjugated cyanodiene synthon and the propensity of such synthons to participate in the olefin metathesis reaction. To this end, we have developed a strategy for the construction of the C11-C15 fragment of borrelidin and demonstrated the utility of the RCM reaction in the preparation of the final macrolide. To our knowledge, this is the first example of a RCM with a nitrile functionality on a diene. 相似文献
28.
G.V.M. Sharma J. Janardhan Reddy P. Sree Lakshmi Palakodety Radha Krishna 《Tetrahedron letters》2004,45(41):7729-7732
A practical and efficient electrophilic substitution reaction of indoles with a variety of aldehydes was carried out using catalytic trichloro-1,3,5-triazine (10 mol %) in acetonitrile to furnish the corresponding bis(indolyl)methanes in excellent yields. Similarly, sugar derived aldehydes gave hitherto unknown bis(indolyl)glycoconjugates in very good yields. 相似文献
29.
Krishna Gopal Dongol M. Cristina Melo e Silva Kouki Matsubara Taisuke Matsumoto Shuntaro Mataka Thies Thiemann 《无机化学与普通化学杂志》2003,629(6):945-947
The preparation of two η6‐estra‐1, 3, 5(10), 6‐tetraene tricarbonylchromium complexes 4 and 6 are described. In both cases only one stereoisomer can be isolated, in contrast to other estrane‐tricarbonylchromium complexes, where complexations are non‐stereoselective. X‐ray crystal structural analysis of 4 discloses that only the more sterically hindered β‐facial isomer is formed. It is assumed that the 6, 7‐olefinic moiety exerts a directive influence on the complexation. 相似文献
30.
The condensation products of 5-amino-1,3-disubstituted-pyrazoles with aromatic aldehydes were identified as 2,4-dihydro-2,5-diphenyl-4-(phenylmethylene)-3H-pyrazol-5-imine derivatives Treatment of these products with mercaptoacetic acid gave new fluorine containing 1H-pyrazolo[3,4-e][1,4]thiazepin-7-ones. 相似文献