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A new pterocarpan, (+)-3,4-dihydroxy-8,9-methylenedioxypterocarpan [1], was isolated from the flowers of Petalostemon purpureus by a DNA strand-scission assay-guided fractionation procedure. Compound 1 demonstrated activity in a standard in vitro DNA strand-scission assay, and cytotoxicity toward a KB tumor cell line. Two other related pterocarpans [2, 3] isolated from same plant were found to be moderately active for KB cells, but were inactive in the DNA strand-scission assay. (+)-4-Hydroxy-3-methoxy-8,9-methylenedioxypterocarpan [2] has not been reported previously as a natural product, while (+)-maackiain [3] has been isolated only as an optically inactive racemate along with its optical antipode, the (-)-isomer.

Ethyl acetate and aqueous extracts of tannin-containing topoisomerase inhibitory plant samples were subjected to one or more of seven tannin removal procedures, and the resulting products were subsequently evaluated for topoisomerase inhibitory activity. In most of the samples investigated, the initial activity was lost after tannin removal. It was concluded that the activity initially observed was primarily due to tannins. Procedures are presented for routinely obtaining tannin-free organic and aqueous fractions.

A new potently sweet labdane diterpene arabinoside, gaudichaudioside A (1), was isolated from the aerial parts of Baccharis gaudichaudiana DC. (Compositae). Also isolated were four other novel labdane arabinosides, gaudichaudiosides B–E (2–5), which although closely related to 1 structurally, were not found to be highly sweet.

Description d'un protocole de separation d'un certain nombre de composes potentiellement edulcorants extraits de Stevia rebaudiana (glycosides), Polypodium glycyrrhiza (polypodosides) et Lippia dulcis (hernandulcine) et comparaison avec l'hernandulcine de synthese

Investigation of the aerial parts of Baccharis gaudichaudiana has afforded a new labdane arabinoside with a novel 23-carbon aglycone skeleton. The structure of this compound, to which we have accorded the trivial name, gaudichaudioside F, was established by analysis of its spectroscopic parameters.

The rootwood of Aeschynomene mimosifolia Vatke (Leguminosae) has yielded a new neoflavonoid, mimosifoliol (1), and an unusual C16-styrylcycloheptenone derivative, mimosifolenone (2). The structures of these compounds were determined on the basis of spectral analysis. Compound 1 demonstrated weak activity in DNA-strand scission assay, while compound 2 was found to be inactive. Mimosifoliol (1) was inactive toward several human cell lines, while 2 was moderately active against the KB cell line.

A new polyacetylenic diepoxide compound, gummiferol [1] was isolated from the leaves of Adenia gummifera by KB cytotoxicity-guided fractionation. Compound 1 exhibited significant activity against the KB human cell line and a broad cytotoxic spectrum against other human cancer cell lines. The structure of 1 was established primarily on the basis of its spectral data.

Publisher Summary This chapter focuses on the structure-activity relationship of highly sweet natural products. It may be seen that ongoing research activities on the isolation and characterization of naturally occurring sweet principles have continued to afford many novel molecules in several structural classes. These compounds occur in species representing a taxonomically wide range of plant families. Methodology has been developed in terms of candidate plant selection, dereplication of sugars, polyols and sweet phenylpropanoids, and in other phytochemical procedures, such that significant progress can be made in the elucidation of further highly sweet-tasting molecules with only a modest investment of capital. To being used in an unmodified form as sweeteners, plant-derived sweet-tasting molecules can serve as useful lead molecules for synthetic optimization. Therefore, knowledge of structure-sweetness relationships of plant sweeteners, and their naturally occurring congeners and semi-synthetic analogs is of use in assisting with the rational design of new sweeteners based on natural product leads.

Three new labdane diterpenes, gaudichaudols A-C [1-3], a new clerodane diterpenoid, gaudichaudone [4], and the known clerodane, articulin acetate [5] have been isolated from the aerial parts of Baccharis gaudichaudiana, together with the known compounds, apigenin, hispidulin, spathulenol, and ursolic acid. Through the application of 1D- and 2D nmr spectroscopy, the structures of the new diterpenoids [1-4] were, in turn; elucidated as 15,16,18,19-tetrahydroxylabd-5-ene, 15-O-acetyl-16,18,19-trihydroxylabd-5-ene, 16-O-p-trans-coumaroyl-15,18,19-trihydroxylabd-5-ene, and 2 beta-hydroxy-15,16-epoxycleroda-1(10),15,16-trien-18,19-olide++ +. The isolated compounds were evaluated in P-388 lymphocytic leukemia cells as well as a battery of human cancer cell lines. Among the diterpenoids, gaudichaudol C [3], gaudichaudone [4], and articulin acetate [5] exhibited significant cytotoxic activity against certain cancer cells.

Two new isoflavones, 6,7,8,3',4',5'-hexamethoxyisoflavone and 7,8,3',4',5'-pentamethoxyisoflavone, have been isolated and characterized from the combined root bark and stem bark of Petalostemon purpureus.