Cytotoxic Constituents from the Fruiting Branches of Callicarpa americana Collected in Southern Florida^,1

Abstract

Bioassay-guided fractionation of the combined fruits, leaves, and twigs (fruiting branches) of Callicarpa americana, collected from a plot in a forested area in southern Florida, led to the isolation of six new clerodane diterpenes (1-6) and eight known compounds. The structures of 1-6 [12(S), 16ξ-dihydroxycleroda-3,13-dien-15,16-olide (1), 12(S)-hydroxy-16ξ-methoxycleroda-3,13-dien-15,16-olide (2), 12(S)-hydroxycleroda-3,13-dien-15,16-olide (3), 16 ξ-hydroxycleroda-3,11 (E),13-trien-15,16-olide (4), 3β,12(S)-dihydroxycleroda-4(18),13-dien-15,16-olide (5), and 12(S)-hydroxycleroda-3,13-dien-16,15-olide (6)] were elucidated by interpretation of spectroscopic data and chemical methods. The absolute configuration at C-12 in 1 and 3 was ascertained using the Mosher ester technique. The cytotoxicity of all isolates was tested against a panel of human cancer cell lines, and compounds 1, 4, and 6, and the known compounds genkwanin, 16ξ-hydroxycleroda-3,13-dien-15,16-olide, and2-formyl-16ξ-hydroxy-3-A-norcleroda-2,13-dien-15,16-olide were active (ED 50 <5 μg/mL). However, 1 was found to be inactive against human cancer cells implanted in mice using a hollow-fiber tumor model. Callicarpa americana L. is a shrub native to the southeastern United States. 2 Although the genus has been considered traditionally as a member of the plant family Verbenaceae, molecular and micro-morphological observations have prompted contemporary taxonomic authorities to reclassify Callicarpa as a member of the family Lamiaceae. 3-5 Preparations of the bark of C. americana have been used to treat fever, 6 the leaves to treat dropsy, 7 and the roots to alleviate colic, 8 dysentery, 9 and skin cancer. 10 The roots and branches have been used in preparations intended to relieve malaria, rheumatism, and fever. 8 The leaf essential oils of C. americana have antialgal and mosquito-deterrent properties, and numerous essential oil components have been identified from the leaves of C. americana. [11][12] As part of an ongoing effort to discover novel anticancer agents from plants, 13 a chloroformsoluble extract of the combined fruits, leaves, and twigs of C. americana was investigated, using cytotoxicity against hormone-dependent prostate cancer cells (LNCaP) to guide the isolation of active constituents. This plant material was obtained from a forest plot in southern Florida using a plot-based collection method (briefly reviewed in ref. 13 ).⊥ Dedicated to the late Dr. Kenneth L. Rinehart of the University of Illinois at Urbana-Champaign for his pioneering work on bioactive natural products.*Author to whom correspondence should be addressed. Tel: (614) Results and DiscussionThe dried fruits, leaves, and twigs of Callicarpa americana L. were extracted with methanol and partitioned following a previously described protocol. 14 Based on the cytotoxic activity of the chloroform-soluble portion, bioassay-guided fractionation using a number of chromatographic techniques was carried out, guided by activity against LNCaP cells. This investigation re...

Biologically Active Natural Products of the Genus Callicarpa

“…Various extracts and other preparations of Callicarpa americana L. have been evaluated for biological activity in a number of assay systems, including antiviral potential of the freezedried leaf [85], oviposition inhibition activity of an aqueous leaf extract [83], antialgal activity of the leaf essential oil [82], mosquito bite-deterrent activity of volatile constituents from the leaves [11], and cytotoxicity of a chloroform extract of the combined fruits, leaves and twigs [36]. Ethanolic extracts of C. arborea Roxb.…”

“…An investigation of Callicarpa americana L. as a potential source of anticancer natural products was carried out using bioassay-guided isolation methodology [36]. The configuration of the isolates, including the absolute configuration of the secondary hydroxy groups was determined using a modified Mosher ester methodology [75,78].…”

“…The configuration of the isolates, including the absolute configuration of the secondary hydroxy groups was determined using a modified Mosher ester methodology [75,78]. Using this technique, the C-12 hydroxy group in the side chain of the clerodane-type diterpenes isolated was determined as having an S absolute configuration [36]. In all, six new compounds and eight known compounds were isolated from the chloroform extract of the combined fruits, leaves, and twigs of C. americana L. [36].…”

“…Using this technique, the C-12 hydroxy group in the side chain of the clerodane-type diterpenes isolated was determined as having an S absolute configuration [36]. In all, six new compounds and eight known compounds were isolated from the chloroform extract of the combined fruits, leaves, and twigs of C. americana L. [36]. The structures of the new compounds were elucidated as 3β,12(S)-dihydroxycleroda-4(18),13-dien-15,16-olide (8), 12(S),16ξ-dihydroxycleroda-3,13-dien-15,16-olide (10), 12(S)-hydroxycleroda-3,13-dien-15,16-olide (12), 12(S)-hydroxycleroda-3,13-dien-16,15-olide (13), 12(S)-hydroxy-16ξ-methoxycleroda-3,13-dien-15,16-olide (14), and 16ξ-hydroxycleroda-3,11(E),13-trien-15,16-olide (16) using a range of spectroscopic techniques, including 1D and 2D NMR and accurate mass measurement [36].…”

“…In all, six new compounds and eight known compounds were isolated from the chloroform extract of the combined fruits, leaves, and twigs of C. americana L. [36]. The structures of the new compounds were elucidated as 3β,12(S)-dihydroxycleroda-4(18),13-dien-15,16-olide (8), 12(S),16ξ-dihydroxycleroda-3,13-dien-15,16-olide (10), 12(S)-hydroxycleroda-3,13-dien-15,16-olide (12), 12(S)-hydroxycleroda-3,13-dien-16,15-olide (13), 12(S)-hydroxy-16ξ-methoxycleroda-3,13-dien-15,16-olide (14), and 16ξ-hydroxycleroda-3,11(E),13-trien-15,16-olide (16) using a range of spectroscopic techniques, including 1D and 2D NMR and accurate mass measurement [36]. Of several known compounds isolated in this study, three were previously reported to occur in the genus Callicarpa [calliterpenone (6), euscaphic acid (88), and 5-hydroxy-6,7,4′-trimethoxyflavone (50)] (see Table 3).…”