Catalytic stereoselective glycosylation

A catalytic stereoselective glycosylation method for preparing an α-1,2-cis glycosidic linkage, which method comprises:

• reacting a glycosyl donor of formula (I):
• wherein
• each of R1 and R3 is independently a substituted or an unsubstituted group selected from alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, alkynyl, alkenyl, heteroarylalkyl, heteroalkylaryl, arylalkenyl, allyl, arylalkyl, alkylcarboxyl, arylcarboxyl, trialkylsilyl, diarylalkylsilyl, dialkylarylsilyl, alkoxyalkyl, tetrahydropyranyl, benzyl, and benzoyl, wherein each substituted group can be independently substituted with at least one of alkyl, aryl, heteroaryl, halo, cyano, alkoxy, amino, carboxyl, amide, and ester;
• each of R2 and R4 is independently alkyl, N3 or OR1, wherein R1 is as defined above;
• or
• any two adjacent groups selected from OR1 and R2, OR1 and R4, and OR3 and R4 are linked together to form a 5- to 7-membered cyclic ring, wherein the cyclic ring can be optionally independently substituted with at least one of alkyl, aryl, heteroaryl, halo, cyano, alkoxy, trialkylsilyl, diarylalkylsilyl, amino, carboxyl, amide, and ester group;
• and
• X is a halide selected from Cl, Br, I and F;
• with a glycosyl acceptor in the presence of a base and an isothiourea catalyst of formula (II):
• wherein n is 0 to 3;
• each of R5 and R6 is H, COOR9, CONHR9, CONR9R9, COR9, or a substituted or an unsubstituted group selected from alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, alkynyl, alkenyl, heteroarylalkyl, heteroalkylaryl, arylalkenyl, and arylalkyl, wherein R9 is alkyl or aryl;
• each of R7 and R5 is H, nitrile, nitro, OR9, COOR9, CONHR9, CONR9R9, COR9, SO2R9 or a substituted or an unsubstituted group selected from alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, alkynyl, alkenyl, heteroarylalkyl, heteroalkylaryl, arylalkenyl, and arylalkyl, wherein R9 is alkyl or aryl;
• or
• R5 and R6 and/or R7 and R8 are linked together to form an aliphatic, an aromatic, or a heterocyclic ring, each of which is optionally independently substituted with a group selected from alkyl, aryl, heteroaryl, halo, cyano, alkoxy, amino, carboxyl, amide and ester.