Asymmetric Pauson−Khand Reaction. Cobalt-Mediated Cycloisomerization of 1,6-Enynes in Carbohydrate Templates: Synthesis of Bis-Heteroannulated Pyranosides
作者:José Marco-Contelles
DOI:10.1021/jo961138w
日期:1996.1.1
The Pauson-Khand reaction on the carbohydrate derived precursors 1-6 is reported. We have described for the first time the cobalt-mediated cyclization of some O-branched chain 1,6-enynes in carbohydratetemplates. The resulting bis-heteroannulated pyranosides 17-22 have been obtained in diastereomerically pure form, in moderate to good yield, and in one, simple synthetic operation. These enantiomerically
A simple and efficient strategy for the regio- and stereoselective synthesis of carbon-branched sugar derivatives is described. The successful implementation of Wittigrearrangement on substrates derived by Ferrier rearrangement of various glycals and 3-O-alkenyl glycals is studied extensively. A highly selective [1,2]- or [2,3]-Wittig rearrangement is revealed that provides a novel class of stereodefined
The bromo substituted unsaturated carbohydrates 3a-f were prepared from 3,4,6-tri-O-acetyl-D-glucal by Ferrier reaction with the appropriate allylic or homoallylic alcohol, deacetylation followed by monosilylation with TBDMSCl, and then alkylation with BrCH2CBr=CH2. The N- and C-analogues 4a,b were synthesized by palladium alkylation of the intermediate carbonate with TsNHCH2CBr=CH2 and (MeO2C)(2)CHCH2CBr=CH2, respectively. Treatment of the unsaturated carbohydrates 3a, 4a, and 4b with a catalytic amount of Pd(OAc)(2)/PPh3 in CH3CN/H2O, in the presence of Bu4NHSO4 and NEt3, afforded the tricyclic compounds 5, 6, and 7, respectively. Under the same conditions, the analogue tricyclic compounds 8, 9, and 10 were formed starting from 3b-d. In the case of compounds 3e and 3f, the formation of the bicyclic glucal 11 via an already described beta-alkoxyelimination was only observed. Moreover, trapping of the sigma-alkylpalladium intermediate obtained from 3e with an external nucleophile yielded the 2-deoxy carbohydrate 12 and the 2,3-unsaturated sugar 13, using respectively sodium formate and sodium tetraphenylborate.
Structure-based design, synthesis and antitumoral evaluation of enulosides
作者:Jonh A.M. Santos、Cosme S. Santos、Claudia L.A. Almeida、Thiago D.S. Silva、João R. Freitas Filho、Gardenia C.G. Militão、Teresinha G. da Silva、Carlos H.B. da Cruz、Juliano C.R. Freitas、Paulo H. Menezes
DOI:10.1016/j.ejmech.2017.01.036
日期:2017.3
Enulosides, carbohydrate derivatives containing an alpha,beta-unsaturated carbonyl unit, were designed and obtained in high yields and isomeric purity. All synthesized compounds exhibited antitumoral activity in micromolar range against four tested tumor cells lines, being the best results observed for HL-60 cells. These compounds open new possibilities to prepare an array of more active, site-specific or selective antitumor agents. (C) 2017 Elsevier Masson SAS. All rights reserved.