In this manuscript entitled “Discovery of new triterpene glycosides from Dendrobium
officinale with their α-glucosidase and α-amylase inhibitory activity” the authors Kiem et al have successfully isolated and identified seven new pentacyclic triterpene glycosides (1-7) from the plant Dendrobium officinale along with six reported ones (8-13). The authors have performed adequate number of experiments (1HNMR, 13CNMR, 2DNMR, IR, HRMS) required for the structural elucidation of the unknown compounds with reference to the known ones. Also the isolated compounds were evaluated for their in vitro α-glucosidase and α-amylase inhibitory activities where few of them (Compounds 1-4, 8, and 9) potentially inhibited both α-glucosidase and α-amylase activities with the IC50 values lower than that of the positive control, acarbose. The paper is extremely well presented and the authors have made a detailed study. I find this manuscript appropriate for publication in “RSC Advances”. only after proper addressing of certain concerns summarized below.
1. For the new compounds 1-4 the authors must explain why the glycosidic linkage of arabinose is alpha, although the coupling constant of the anomeric proton at 4.49 ppm is 7.72 Hz.
2. The authors claims that the structure of 1 is similar to that of the known structure 8, except for the presence of the additional caffeoyl group. But IR of compound 1, shows no extra peak due to the presence of conjugated ester as that of 8. Also the authors must explain the extra peak obtained at 1548 cm-1 in compound 3 and 4
3. The authors should check the integration of all the protons in 1H NMR and match them with the structure as some protons are not being integrated (compound 3, peak at 3.21 ppm is not integrated)
4. The authors are suggested to provide the full structure each new compounds over the 1H, 13 CNMR and 2D spectra for a better visualization of the readers.
5. The authors must provide a HPLC spectra of all the newly isolated compounds mentioning their purity percentage
6. In the discussion of compound 7, the authors wrote that “The NMR data of 7 were closely related to those of compound 4 except ..”.I guess it is structure 5 that is more closely related o structure 7.Please verify.
7. The authors must provide the 1HN MR spectra or at least the ESI-MS of the known compounds isolated (8-13)