Four New Pentasaccharide Resin Glycosides from Ipomoea cairica with Strong α-Glucosidase Inhibitory Activity

Six pentasaccharide resin glycosides from Ipomoea cairica, including four new acylated pentasaccharide resin glycosides, namely cairicoside I-IV (1-4) and the two known compounds cairicoside A (5) and cairicoside C (6), were isolated from the aerial parts of Ipomoea cairica. Their structures were established by a combination of spectroscopic, including two dimensional (2D) NMR and chemical methods. The core of the six compounds was simonic acid A, and they were esterfied the same sites, just differing in the substituent groups. The lactonization site of the aglycone was bonded to the second saccharide moiety at C-2 in 1-4, and at C-3 in 5-6. Compounds 1 and 5, 4 and 6 were two pairs of isomers. The absolute configuration of the aglycone in 1-6 which was (11S)-hydroxyhexadecanoic acid (jalapinolic acid) was established by Mosher's method. Compounds 1-4 have been evaluated for inhibitory activity against α-glucosidase, which all showed inhibitory activities.