Tannins from Betel Nuts

From the acetone extract of fresh‐betel nuts, two procyanidin pentamers, two procyanidin tetramers and three procyanidin trimers, along with (+)‐catechin, (‐)‐epicatechin, procyanidin A‐l, procyanidin B‐l, procyanidin B‐2, and procyanidin B‐7 were isolated. Based on 1 H NMR and 13 C NMR spectral data as well as the results of thiolysis degradation, the chemical structures of two series of oligomeric arecatannins A and B have been established. The arecatannins from betel nuts were found to be condensed‐type tannins which possess (‐)‐epicatechin unit and (+)‐catechin units. All arecatannins had C 4 ‐C 8 linked (‐)‐epicatechin in the upper units whereas the (+)‐catechin in the terminal unit had C 4 ‐C 8 or C 4 ‐C 6 linkage.