Complete assignment of ¹H and ¹³C NMR data for nine protopanaxatriol glycosides

Nine protopanaxatriol glycosides isolated from mild acid hydrolysis products of crude root saponins of Panax notoginseng were identified as 20(R)‐ginsenoside‐Rh1, 20(S)‐ginsenoside‐Rh1, ginsenoside‐Rg1, ‐Re and ‐Rg2, notoginsenoside‐R2 and ‐R1, a mixture of 25‐hydroxy‐20(S)‐ginsenoside‐Rh1 and its C‐20 (R) epimer, ginsenoside‐Rh4. The complete assignments of the 1 H and 13 C NMR chemical shifts for these glycosides were obtained by means of 2D NMR techniques, including 1 H– 1 H COSY, ROESY, HMQC, HMBC and HMQC‐TOCSY spectra. The glycosylation shift effect of protopanaxatriol and the differences in chemical shifts between 20(R)‐ and 20(S)‐protopanaxatriol isomers are also discussed. Except for ginsenoside‐Re and ‐Rg2, complete NMR assignments of the other seven glycosides are reported for the first time.