Synthesis of novel photolabile glycosides from methyl 4,6- O-( o-nitro)benzylidene-α- d-glycopyranosides

• Published in: Tetrahedron 2008-11, Vol.64 (47), p.10687-10693
• Main Authors: Zhu, Chen-Jiang, Yi, Hua, Chen, Guo-Rong, Xie, Juan
• Format: Article
• Language: English
• Subjects: C-Glycosides; Carbohydrates; Epimerization; Photolabile protecting groups; Regioselectivity; Ring opening
• ISSN: 0040-4020; 1464-5416
• DOI: 10.1016/j.tet.2008.09.018

Novel photolabile sugar derivatives bearing a 4- or 6- O-( o-nitro)benzyl group have been prepared from the corresponding methyl 4,6- O-( o-nitro)benzylidene α- d-glycopyranosides. Regioselective cleavage with BF 3·Et 2O/Et 3SiH led to the methyl 6- O-( o-nitro)benzyl gluco- and manno-α- d-glycopyranosides 3 and 6. Inversion of configuration at 4-OH position of gluco and manno derivatives offered the otherwise inaccessible methyl 6- O-( o-nitro)benzyl galacto- and talo-α- d-glycopyranosides 4, 5, and 7. Careful reaction with PhBCl 2/Et 3SiH (3 equiv of reagents, 10 min at −78 °C) led to the desired methyl 4- O-( o-nitro)benzyl gluco- and manno-α- d-glycopyranosides 8 and 9 in very good yield. However, prolonged reaction with 6 equiv of PhBCl 2/Et 3SiH transformed the methyl 4,6- O-( o-nitro)benzylidene α- d-glucopyranoside 11 into the reduced d-glucitol derivative 15. Oxidative cleavage of 5,6-diol function of 15 gave the corresponding photolabile l-xylose 17. The photolabile glucosides 3 and 8 have been further transformed into the photolabile α- C-allyl d-glucopyranosides 20 and 22. [Display omitted]