Minor alkaloids from an aqueous extract of the hook-bearing stem of Uncaria rhynchophylla

Abstract

Seven new monoterpene alkaloids (1 − 7), along with 16 known analogues, were isolated from an aqueous decoction of the hook-bearing stems of Uncaria rhynchophylla (Gou-teng). Their structures were determined by spectroscopic data analysis, single crystal X-ray diffraction, and electronic circular dichroism (ECD) calculations. Compounds 1 and 2 are stereoisomers belonging to a novel type of pseudoindoxyl monoterpene alkaloids, 3 is the first monoterpene furoindole alkaloid from nature, and 4 − 7 are derivatives of the known monoterpene alkaloids featuring different structures.

Graphical Abstract

Keywords:

• Rubiaceae
• Uncaria rhynchophylla
• monoterpene alkaloid
• pseudoindoxyl alkaloid
• uncarpseudoindosides
• furorhynchophylloside
• secorhynchohyllic acids
• 18-dehydroisorhynchophyllic acid

Acknowledgements

We dedicate this paper to Prof. Yu Dequan in commemoration of his life-time contribution to natural products researches.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Financial support from the National Natural Sciences Foundation of China [grant nos. 82293681 and 82293685 (82293680)] and CAMS Innovation Fund for Medical Science 2022-I2M-2-002 and 2021-I2M-1-028 is acknowledged.