Sheng-Xiang Qiu

Computer-assisted structure elucidation: application of CISOC-SES to the resonance assignment and structure generation of betulinic acid

The application of a computer‐assisted structure elucidation expert system, CISOC–SES, leading to the unequivocal 1H, 13C and NOE resonance assignment of betulinic acid, a biologically active triterpenoid with complicated NMR resonances, is described. The procedure consists of peak picking that is independent of background information, systematic interpretation of connectivity information from 2D NMR into bond constraints and resonance assignment based on the proposed structure. De novo structure generation based solely on the molecular formula and spectral data is also described. This application demonstrates the potential of efficient and systematic structure elucidation of natural products with modern high‐resolution NMR spectroscopy combined with artificial intelligence.

Antimalarial Agents from Plants II. Decursivine, A New Antimalarial Indole Alkaloid from Rhaphidophora decursiva

Antimalarial bioassay-directed fractionation led to the isolation of a new active indole alkaloid, decursivine (1), from the leaves and stems of Rhaphidophora decursiva Schott (Araceae). In addition, a leaf sample yielded the structurally-related compound serotobenine (2), previously reported from a taxonomically unrelated family, which was not active against Plasmodium falciparum. The structure of 1 was elucidated by spectroscopic means, and its antimalarial activity was observed with IC 50 values of 3.93 and 4.41µg/ml against the D6 and W2 clones of Plasmodium falciparum, respectively.

Vitexlactam A, a novel labdane diterpene lactam from the fruits of Vitex agnus-castus

A novel labdane diterpene alkaloid, vitexlactam A (1) was isolated as a prism from the n-hexane extract of the fruits of Vitex agnus-castus through normal and reverse phase column chromatography. Its structure was elucidated to be 6beta-acetoxy-9alpha-hydroxy-13(14)-labden-16,15-amide, based on chemical and spectral evidences including 1D and 2D NMR spectra. The structure was confirmed by X-ray crystallographic analysis. Compound 1 is the first naturally occurring labdane diterpenoid containing an alpha,beta-unsaturated gamma-lactam moiety

Polyacetyleneginsenoside-Ro, a novel triterpene saponin from Panax ginseng

A new oleanolic acid-derived saponin, polyacetyleneginsenoside-Ro (1), was isolated along with the known ginsenosides-Ro methyl ester (2), -Rf, -Rg1, -Rg2, and gingerglycolipid B from the roots of Panax ginseng C. A. Meyer. The new saponin was identified as a ginsenoside-Ro derivative containing a polyacetylene side chain by spectroscopic means including 1D and 2D NMR, and was found to inhibit the replication of human immunodeficiency virus type 1 (HIV-1) with an IC50 value of 13.4 μg/mL (11.1 μM).

Acylated C-21 steroidal bisdesmosidic glycosides from Caraluma umbellata

From the whole plant of Caraluma umbellata, three new C-21 steroidal glycosides, named as carumbellosides III-V, were isolated and their structures elucidated by extensive spectroscopic experiments, devoid of any derivatisation, as caralumagenin 3-O-beta-D-glucopyranosyl(1-->4)-beta-D-digitalopyranoside-20-O-be ta- D-glucopyranoside, caralumagenin 3-O-beta-D-glucopyranosy(1-->4)- beta-D-digitalopyranoside-20-O-(2-O- benzoyl)-beta-D-glucopyranoside and caralumagenin 3-O-[6-O-benzoyl-beta-D-glucopyranosyl(1-->4)]-beta-D- digitalopyranoside-20-O-(2-O-benzoyl)-beta-D-glucopyranoside. The determination of the absolute configuration of the aglycone as (20 R), the conformations of the sugars and the unambiguous assignments of their NMR spectroscopic signals were achieved by a combination of 2D-NMR techniques. The isolates were devoid of significant cytotoxity in the UIC human cancer cell panel.

Bisdesmosidic pregnane glycosides from Caralluma lasiantha

Abstract From the whole plant of Caralluma lasiantha , two new bisdesmosidic C-21 steroidal (pregnane) glycosides, named as lasianthoside-A and -B, were isolated and their structures elucidated solely based on extensive 2D-NMR and MS/MS spectral analysis as caralasigenin 3- O -β- d -glucopyranosyl(1→4)-β- d -digitalopyranoside-20- O -α- l -rhamnosyl(1→6)-β- d -glucopyranoside and caralumagenin 3- O -β- d -glucopyranosyl(1→4)-β- d -digitalopyranoside-20- O -α- l -rhamnosyl(1→6)-β- d -glucopyranoside. In addition, a known flavonoid glycoside, luteolin neohesperidoside, was also isolated.

Steroidal glycosides from the subterranean parts of Liriope spicata var. prolifera

In a continuation of phytochemical studies on the underground organs of Liriope spicata var. prolifera, four new steroidal glycosides, lirioproliosides A-D, along with two known compounds, 25(S)-ruscogenin 1-O-[alpha-L-rhamnopyranosyl(1-->2)[beta-D-xylopyranosyl (1-->3)]-beta-D-fucopyranoside and ophiopogonin A, were identified. The structures of lirioproliosides A-D were established by a combination of spectroscopic and chemical methods as 25(S)-ruscogenin 1-O-[alpha-L-rhamnopyranosyl(1-->2)][beta-D-xylopyranosyl (1-->3)]-beta-D-fucopyranoside-3-O-alpha-L-rhamnopyranoside, 25(S)-ruscogenin 1-O-[3-O-acetyl-alpha-L-rhamnopyranosyl(1-->2)]-beta-D-fucopyranoside, 25(S)-ruscogenin (1-O-[2-O-acetyl-alpha-L-rhamnopyranosyl (1-->2)]-beta-D-fucopyranoside and ruscogenin (1-O-[2-O-acetyl-alpha-L-rhamnopyranosyl(1-->2)]-beta-D-fucopyranoside, respectively. Among these steroidal glycosides, ophiopogonin A and lirioprolioside B, and lirioproliosides C and D, were isolated as epimeric pairs.

A pregnane steroid from Aglaia lawii and structure confirmation of cabraleadiol monoacetate by X-ray crystallography

The pregnane steroid, (E)-aglawone, along with four known triterpenes, and a known sterol mixture were isolated from the bark of Aglaia lawii (Wight) Saldanha ex Ramamoorty (Meliaceae). The structural determination/identification was accomplished by a combination of 1D- and 2D-NMR spectroscopic techniques. The relative stereochemistry of the known triterpene, 20S,24S-epoxydammarane-3alpha,25-diol acetate, was also unequivocally determined for the first time by X-ray crystallography. The isolates were not active against various human cancer cell lines.

Crystal and molecular structures of a natural equimolecular mixture of two epimeric diterpenes

Irroratin A (1), isolated from the aerial Darts of Isodon irrorata (Forrest.) (Labiatae), was shown to be an equimolecular mixture of two C-20 epimers of a new ent-kaurene diterpene both in the crystalline state and pyridine solution, based on X-ray, LC/MS/MS, FABMS as well as extensive 1D- and 2D-NMR spectral analysis. The two epimers were hound together by hydrogen bonds, and when in chloroform and methanol solution, the 20S-epimer predominates. Irroratin A exhibited potent cytotoxicity against several human cancer cell lines

Patuletin-3-O-Rutinoside from the Aerial Parts of Echinacea angustifolia

The major flavonoid of the aerial parts of Echinacea angustifolia was found to be patuletin-3- O -rutinoside (1), rather than rutin (2), as reported previously. The related amount of patuletin-3- O -rutinoside is 5-8-times higher than that of rutin in the tested samples. Patuletin-3- O -rutinoside also existed in the aerial parts of E. purpurea and E. pallida, and the first complete NMR assignment of patuletin-3- O -rutinoside was made by using 2D NMR techniques. This is the first report of the occurrence of patuletin-3- O -rutinoside in Echinacea species.