Complete 1H and 13C NMR assignments of a series of pergalloylated tannins

Tannins are secondary metabolites widely distributed in the plant kingdom. A common feature of tannins is their phenolic units, which can be linked together to form highly diverse chemical structures. Because these compounds constitute an important fraction of the food and beverage ingested, they have been thoroughly studied for their biological effects. Recently, we have performed a phytochemical study on Cornus canadensis, an abundant flowering plant growing wild in North America and giving edible fruits. A preliminary bioactivity screening was performed and revealed that an extract from C. canadensis was active toward Herpes simplex virus type 1. Following bioassay-guided fractionations, hydrolyzable tannins were identified. One of these compounds, namely, 1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose (PGG), has been the subject of several pharmaceutical studies as recently reviewed by Zhang. The biological and medicinal properties of PGG are diverse and include anticancer, antioxidant, antimutagenic, anti-inflammatory, anti-allergic, hypocholesterolemic, anticoagulation, antinephrolithiasis, anticonvulsion, antiviral, and antibacterial activities. Furthermore, a series of PGG analogs were synthesized and found to be an optimal scaffold to stimulate glucose transport in adipocytes. Some of these compounds were also prepared in our laboratory in order to assess their antiherpetic activities. Because these analogs were only partially characterized by NMR, we would like to report herein the complete H and C assignments of pergalloylated D-glucose (1), D-mannose (2), Dgalactose (3), D-xylose (4), L-ribose (5), L-arabinose (6), L-rhamnose (7), and D-fucose (8) by using a combination of one-dimensional and two-dimensional NMR experiments.