R. Verdtryn et ul. / Polymer-supported solution synthesis of u heptuglucosideRed. Trnv. Chim. Pays-Bas 112, 464-466 (1093) 0 165-05 13/93/7/8464-03$6.00 April 26, 1993) Abstract. An efficient synthesis of methyl heptaglucoside 2 using poly(ethy1eneglycol)monornethyl ether as a polymer support is described. Elongation of the acceptor 11, anchored via a succinoyl linkage to PEG, with the appropriate glycosyl donors 4-6 and intermittent protective group manipulations gave fully protected heptamer 18. Deprotection of 18 furnished, after purification as its peracetate, title compound 2 in a good overall yield.
Preliminary Communication
POLYMER-SUPPORTED SOLUTION SYNTHESIS OFIt is now well established' that the branched and plinked glucoheptaose 1 triggers the production of phyte alexins by binding to a recepto? tethered in soybean membranes. With the objective to gain a detailed insight into the structural requirements3 for optimal interaction of the methyl analogue of 1 (i.e. compound 2)4 with the plant receptor, the availability' of a wide range of modified heptasaccharides would be desirable. In order to meet this requirement, we developed6 an efficient and high yielding route to the heptaglucoside 2 based on the retrosynthetic scheme depicted below. However, the recurrence of work up and purification steps renders the synthesis of 2 and analogues thereof rather laborious and time-consuming.Recently, Krepinsky el a1.' reported the preparation of disaccharides using pol y(eth yleneglycol)monomethyl ethe?(PEG) as a polymer support. A characteristic fcature of the PEG-methodology, recently applied by Bonora et ~1 .~ for the rapid and large-scale synthesis of oligonucleotides, is the fact that the coupling product resulting after each elongation step can be collected by simple precipitation, thus nullifying the earlier mentioned disadvantages of a solution methodology of oligosaccharide synthesis. In order to achieve our goal, we adopted the following crucial elements of the in our laboratory devised6 successful synthetic route to the target molecule 2. Thus, the same terminal (i.e. monomer 6) and non-terminal (i.e. dimer 4 and monomer 5) synthons, all of which contain a participating benzoyl group at C-2 to secure the stereocontrolled construction of p-glycosidic linkages, will be used. In addition, the reliable regioseleciive glycosylation of the primary hydroxyl of the 4,6-diol function, generated after deblocking of the benzylidene protecting group from adducts derived from the iodoniumpromoted elongation of dimer 4 at the anomcric centre, plays a pivotal role in the PEG-supported synthesis of 2.The assembly of 2 commences, as delineated in Scheme 1, with the stepwise immobilization" of methyl 2,3-di-0-benzoyl-a-D-glucopyranoside" (7) to PEG. Thus, tritylation of 7 with 4,4'-dimethoxytrityl (DMT) chloride, and subsequent treatment of 8 with succinic (SUC) anhydride in the presence of 4-(dimethy1amino)pyridine (DMAP) gave the Suc derivative 9. The anchorage of 9 to the hydroxyl function of PEG was readily effe...
