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51.
Jamin Huang Dean F. Bushey Michael D. Graves Brenda F. Johnson Dianne D. Singleton 《Journal of heterocyclic chemistry》1987,24(1):1-7
A series of 3-substituted-5-methoxy-1,3,4-oxadiazol-2-ones were prepared from aldehydes, ketones, phenylacetic acids, and 1,2- and 1,3-diketones. Conditions for the formation of these oxadiazolones from the precursor N-carbamoyl chlorides depended on the structure, and varied from spontaneous ring closure to those requiring bases. Variation in the N-3 substituents sometimes produced mixtures of isomers which were separated and identified. These molecules were prepared in order to study the effect of the N-3 substituent variation on the biological properties of oxadiazolones. 相似文献
52.
Leslie C. Damude Philip A.W. Dean Michael D. Sefcik Jacob Schaefer 《Journal of organometallic chemistry》1982,226(2):105-114
The cross-polarization magic angle spinning 13C NMR spectra of Hg(SbF6)2 - 2 Arene (Arene = C6HMe5, 1,2,4,5-C6H2Me4, 1,2,3,4-C6H2Me4, or C6H6) have been measured. The spectra of the complexes of C6HMe5 and 1,2,4,5-C6H2Me4 are consistent with static η1-bonding of the mercury to the arene at an unsubstituted carbon atom, while the spectra of the 1,2,3,4-C6H2Me4 and C6H6 complexes show the arene to have time-averaged Cs or C2, and C6 symmetry respectively, at the temperature of measurement (300 K).The reduced temperature 13C NMR spectra of Hg(Arene)n2+ (n = 1 or 2; Arene = 1,3,5-C6H3R3 (R = Me, i-Pr, or t-Bu)) in SO2 solution are also reported and affirm that in these intramolecularly mobile species the mercury bonds in an η1-manner, with unsubstituted aryl carbon atoms being the strongly preferred point of mercury attachment. This site preference is further demonstrated by the solution 13C NMR spectra of Hg(Arene)n2+ (Arene = 1,2,3,4-C6H2-Me4, n = 1 or 2; Arene = 1,4-C6H4R2, R = Me or t-Bu, n = 1). The spectra of the 1,4-C6H4R2 complexes and Hg(p-C6H4-t-BuMe)2+ provide clear evidence for steric influence of the binding site.Like Hg(C6Me6)22+, but unlike most of the complexes of substituted benzenes which have been studied, Hg(1,3,5-C6H3-i-Pr3)22+ exchanges only slowly with excess free ligand. 相似文献
53.
A convergent total synthesis of the marine natural product dysiherbaine was accomplished. The key steps of the synthesis are an alkylation at the gamma-carbon of a protected glutamate with a highly substituted pyran derived from mannose, which was followed by a ring-contraction cascade reaction, which simultaneously gave the tetrasubstituted carbon and the hexahydrofuro[3,2-b]pyran ring system of the natural product. 相似文献
54.
Resibufogenin is a cytotoxic steroid isolated from the Chinese drug ChanSu. The biotransformation of resibufogenin by Mucor polymorphosporus afforded 22 products, and 15 of them were new. The transformation reactions involved hydroxylations at C-1β, C-5, C-7α, C-7β, C-12α, C-12β and C-16α, as well as epimerization or dehydrogenation of 3-OH. Hydroxylations at C-12α, C-12β and C-16α were the major reactions, each giving products in >5% yields, whereas the other products were obtained in fairly low yields. Some of the products showed decreased but still potent cytotoxicities. This investigation provided a useful approach to prepare new bufadienolides and most of them were difficult to obtain by chemical means. 相似文献
55.
α-Oxo-carboxylic acids undergo photo-oxidative decarboxylation from both C-1 and C-2 positions, and reaction does not involve singlet oxygen: a mechanism involving an electron transfer reaction is postulated. 相似文献
56.
57.
Miao Yang Shannon J. Odelberg Zongzhong Tong Dean Y. Li Ryan E. Looper 《Tetrahedron》2013,69(27-28):5744-5750
Cationic Rh(II) complexes are able to catalyze the regioselective hydroamination of propargyl ureas in a 6-endo fashion. This transformation permits access to interesting substitution patterns of dihydropyrimidines, which have found use as nucleotide exchange factor inhibitors. 相似文献
58.
59.
Rajeev Rajasekharan‐Nair Dean Moore Dr. Kirsten Chalmers Dr. Dawn Wallace Louise M. Diamond Lisa Darby Dr. David R. Armstrong Dr. John Reglinski Dr. Mark D. Spicer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(7):2487-2495
The alkylation reactions of soft scorpionates are reported. The hydrotris(S‐alkyl‐methimazolyl)borate dications (alkyl=methyl, allyl, benzyl), which were prepared by the reaction of TmMe anion and primary alkyl halides, have been isolated and structurally characterised. The reaction is, however, not universally successful. DFT analysis of these alkylation reactions (C?S versus B? H alkylation) indicates that the observed outcome is driven by kinetic factors. Extending the study to incorporate alternative imine thiones (mercaptobenzothiazole, bz; thiazoline, tz) led to the structural characterisation of di[aquo‐μ‐aquohydrotris(mercaptobenzothiazolyl)boratosodium], which contains sodium atoms in the κ3‐S,S,S coordination mode. Alkylation of Na[Tbz] and Na[tzTtz] leads to decomposition resulting in the formation of the simple S‐alkylated heterocycles. The analysis of the species involved in these reactions shows an inherent weakness in the B? N bond in soft scorpionates, which has implications for their use in more advanced chemistry. 相似文献
60.
Dr. Dean Strotz Dr. Julien Orts Dr. Harindranath Kadavath Dr. Michael Friedmann Dhiman Ghosh Dr. Simon Olsson Dr. Celestine N. Chi Aditya Pokharna Prof. Dr. Peter Güntert Dr. Beat Vögeli Prof. Dr. Roland Riek 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(49):22316-22323
Protein allostery is a phenomenon involving the long range coupling between two distal sites in a protein. In order to elucidate allostery at atomic resoluion on the ligand-binding WW domain of the enzyme Pin1, multistate structures were calculated from exact nuclear Overhauser effect (eNOE). In its free form, the protein undergoes a microsecond exchange between two states, one of which is predisposed to interact with its parent catalytic domain. In presence of the positive allosteric ligand, the equilibrium between the two states is shifted towards domain–domain interaction, suggesting a population shift model. In contrast, the allostery-suppressing ligand decouples the side-chain arrangement at the inter-domain interface thereby reducing the inter-domain interaction. As such, this mechanism is an example of dynamic allostery. The presented distinct modes of action highlight the power of the interplay between dynamics and function in the biological activity of proteins. 相似文献