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In an attempt to study the structural dependence of antimycobacterial activity of the guaianolide dehydrocostus lactone and its derivatives, m-chloroperoxybenzoic acid oxidations of dehydrocostus lactone (1a) were performed. Three new monoepoxides, one previously synthesized diepoxide, and two new diepoxides were obtained. Two of the monoepoxides are C-10 epimers (3a, 3b), while the 4(15)-monoepoxide (2) has the 4α-O-configuration. The known diepoxide (4a) contains a C-10 α-epoxide and a β-epoxide at C-4. The diepoxides 4b and 4c, each with a C-4 α-epoxy group, differ in the configuration of the epoxide ring at C-10. Allylic oxidation of dehydrocostus lactone (1a) with selenium dioxide/tert-butyl hydroperoxide afforded the known 3-epizaluzanin C (1b). The relative configurations of compounds 1b−4c were established by 1D and 2D NMR techniques (¹H, ¹³C, COSY, NOESY, HMQC, and HMBC) as well as comparison with literature data. The molecular structures of lactones 1b, 4a, and 4c were determined by single-crystal X-ray diffraction. In radiorespirometric bioassays against Mycobacterium tuberculosis and Mycobacterium avium, dehydrocostus lactone (1a) exhibited minimum inhibitory concentrations of 2 and 16 μg/mL, respectively. In contrast, its monoepoxides (2, 3a, and 3b) and diepoxides (4a−c), as well as its hydrogenated derivatives and other analogues (1b, 1c, 5, and 6), showed significantly lower activities against M. tuberculosis.

In continuation of our phytochemical investigation of Illicium floridanum Ellis (American star anise, star bush), three new sesquiterpene lactones possessing the anisatin−type carbon skeleton (8,9-seco-prezizaane skeleton), 14-acetoxy-3-oxofloridanolide (1), 13-acetoxy-14-(n-butyryloxy)floridanolide (2), and 3β-acetoxy-14-n-butyryloxy-10-deoxyfloridanolide (3), were isolated from fruits of this plant. Their structures were elucidated by 1D and 2D NMR measurements. The molecular structure of 1 was obtained by single crystal X-ray diffraction. The 11,3-δ-lactone structure of the compound previously described as debenzoyldunnianin in our previous communication, on grounds of NMR spectral evidence and X-ray crystallographic analysis is revised to a δ-lactone closed between C-11 and C-7 (compound 4). The neurotoxic sesquiterpene lactone anisatin (5) and its isomer 2α-hydroxyneoanisatin (3-deoxy-2α-hydroxyanisatin, 6) were also isolated and identified by spectroscopic means. The presence of the neurotoxin 5 in relatively high amounts in the fruits and leaves confirms and explains early reports on the toxicity of this plant.

The sesquiterpene lactones dunnianin (1), debenzoyldunnianin (2), 7-deoxy-7-oxodunnianin (3), and pseudoanisatin (4) were isolated from fruits of Illicium floridanum. On the basis of the molecular structure of 4, 1−3 had previously been assigned structures containing 11,14-ɛ-lactone rings (1a−3a). Due to inconsistencies in the ¹H-NMR spectra of 1−3, when compared with the spectrum of 4, their structures were reinvestigated by NMR spectroscopic analyses, and the molecular structure of 1 was determined by single-crystal X-ray diffraction. Compounds 1−3 were found to contain an 11,3-δ-lactone ring instead of the previously reported 11,14-ɛ-lactone, which required revision of their structures from 1a−3a to 1b−3b, respectively.

The structures of the known limonoids harrisonin (1) and 12β-acetoxyharrisonin (2), isolated from the root bark of Harrisonia abyssinica, were reanalyzed by modern 1D and 2D NMR spectroscopic methods, and the molecular structure and relative configuration of 12β-acetoxyharrisonin were determined by single-crystal X-ray diffraction. The spectral findings obtained require revision of the structures of these compounds from 1 and 2 to 3 and 4, respectively. The new molecular structures 3 and 4 display a novel limonoid skeleton with a unique five-membered ring B.

In a bioassay-guided search for antimycobacterial compounds from higher plants of the southeastern United States, we have chemically investigated the sea daisy (Borrichia frutescens) from coastal marshes of Louisiana for their active constituents. Bioactive chromatographic fractions provided two new triterpenes, (24R)-24,25-epoxycycloartan-3-one (1) and (23R)-3-oxolanosta-8,24-dien-23-ol (4), and (3αH,24R)-24,25-epoxycycloartan-3-ol (3a). Compound 3a had been previously isolated as a mixture of C-24 epimers. The structures of 1, 3a, and 4 were established by spectroscopic methods and chemical transformations, and the molecular structures of 1 and 4 were determined by single-crystal X-ray diffraction. In a radiorespirometric bioassay against Mycobacterium tuberculosis, the epoxycycloartanes 1 and 3a exhibited minimum inhibitory concentrations of 8 μg/mL. In contrast, the lanostadiene-type triterpene 4 showed no significant inhibition at 128 μg/mL, as did the acetate 3b. Cytotoxicity for Vero cells gave IC50 values of 71.8, 39.8, and 103.6 μg/mL for triterpenes 1, 3a, and 4, respectively.

In a bioassay-guided search for antimycobacterial compounds from higher plants, we have chemically investigated methanolic extracts of seeds of Melia volkensii. Chromatographic fractions provided two new euphane (20R)-type triterpenoids. The structures of the new compounds, 12β-hydroxykulactone (1) and 6β-hydroxykulactone (2), were elucidated by 1D and 2D NMR (¹³C, ¹H, ¹H−¹H COSY, HMQC, HMBC, and NOESY spectra) and FABMS studies and shown to be hydroxyl derivatives of kulactone (3). Also isolated was the known kulonate (4). In a radiorespirometric bioassay against Mycobacterium tuberculosis, compounds 1, 2, and 4 exhibited minimum inhibitory concentrations of 16, 4, and 16 μg/mL, respectively.