Bioactive constituents from Robinia pseudoacacia L. (Fabaceae)
Abstract
The purpose of this study was to identity novel bioactive organic chemical constituents from the ethanolic extracts of the black locust tree, Robinia pseudoacacia L. (Fabaceae). Screening assays demonstrated that these extracts had significant activity in the brine shrimp lethality test (BST) and human tumor cytotoxicity assays (MTIF assays); in addition, the species has had many interesting folkloric medicinal uses. However, the bioactive principles of the plant had not been identified; thus, the current bioactivity-directed phytochemical study was initiated. The ethanolic extracts of the dried and pulverized whole plant material were subjected to a sequence of partition, flash column chromatography and high performance liquid chromatography, with the BST directing the fractionation. Twelve (1–12) biologically active compounds were isolated, and their structures, including stereochemistries, when necessary, were determined by vigorous spectral analyses on the parent compounds as well as their derivatives. The structural elucidation strategies included UV, FT-IR, low resolution and high resolution CI/EI MS, 1D (1H, 13C, APT, DEPT and difference NOE) and 2D-NMR (COSY, HMQC, HMBC, NOESY and ROESY), Mosher ester methodology and X-ray crystallographic analysis. These compounds are structurally diverse and represent five different structural types. Acacetin (1), secundiflorol I (2), mucronulatol (3), isomucronulatol (4) and isovestitol (5) are flavonoids. Robinspirols A–C ( 6–8) have unique spiro-magstigmane skeletons. Robinlin ( 9) is an unusual homo-monoterpene. Robinpiramic acid (10) is a diterpene. Abrisapogenol E (11) and abrisapogenaldacetal (12) are triterpenes. Compounds 2–5 are, for the first time, reported for the species; and compounds 6–10 and 12 are new to the literature. All of the isolated compounds (1–12) were tested in the BST and MTT cytotoxicity assays. All of them demonstrated good activities in the BST. Compounds 3 and 5 were generally, but weakly, cytotoxic against all of the six human solid tumor cell lines tested (A-549, MCF-7, HT-29, A-498, PC-3 and PACA-2). 1 and 10 were selectively and significantly cytotoxic against the PC-3 (prostate) and PACA-2 (pancreatic) cell lines, respectively. Compounds 2, 4 and 6–11 did not show significant cytotoxicities in the cell lines tested. Their BST activities, however, suggest that the possibilities are high that these compounds possess pharmacological activities other than cytotoxicities.* *Please refer to dissertation for diagrams.
Degree
Ph.D.
Advisors
McLaughlin, Purdue University.
Subject Area
Analytical chemistry|Organic chemistry
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