Trichotomol, a New Cadinenediol from Cordia trichotoma

Um novo sesquiterpeno, nomeado trichotomol e compostos conhecidos como cordiacromo C, α-cadinol, ácido oleanólico, oncocalyxona A, β-sitosterol, glicosídeo do β-sitosterol, alantoína e sacarose foram isolados a partir do extrato etanólico do cerne de Cordia trichotoma. Suas estruturas foram determinadas por análises espectroscópicas e comparação com dados publicados para compostos estruturalmente relacionados.


Introduction
Cordia trichotoma Vell.(Boraginaceae) is a tropical tree, popularly known as "frei jorge" 1 .According to a literature survey, several uses in traditional medicine such as cicatrizant, astringent, anti-inflammatory, antihelminthic, antimalarial, diuretic and to treat urinary infections, lung diseases and leprosy have been reported for several Cordia species [2][3][4] .No medicinal use has been reported for C. trichotoma, but its wood is recognized for its durability in carpentry and construction 1 .Previous phytochemical investigations of plants from this genus have described several natural products structurally related to terpenoid quinone and hydroquino-nes 5- 7 .In the last few years, several articles have been published on this kind of compounds, from Auxemma genus [8][9][10] , belonging to the same family and formerly considered synonimous of Cordia.To the best of our knowledge, except for a publication in which the presence of eudesmol isomers from C. trichotoma wood 11 has been recorded, there have been no other reports of any similar chemical investigation in the literature.In this paper we describe the isolation and structure elucidation of the known compounds: β-sitosterol, sitosterol-β-D-glucoside 12 , oleanolic acid 13 , allantoin 14 , sucrose 15 , α-cadinol 16 , oncocalyxone A 8 , cordiachrome C 5 , and a new sesquiterpene, trichotomol (1).Although cordiachrome C (2) had been previously isolated from C. millenii, only the partial 1 H NMR data was provided but some doubt about its stereochemistry 5 has remained.Here the complete 1 H and 13 C spectral data and assignments for 2 are reported for the first time and used to corroborate the stereochemical aspects.
The molecular formula C 15 H 26 O 2 , which indicates three double-bond equivalents, was deduced using EIMS, 13 C NMR, and DEPT analyses.The 13 C NMR (BB and DEPT) spectra displayed signals corresponding to four methyl, four methylene, four methine, and three nonhydrogenated carbons.Resonances due to two olefinic carbons at δ C 134.3 (C) and 124.7 (CH) in the 13 C NMR spectrum accounted for one double-bond equivalent, e-mail: otilia@dqoi.ufc.brsuggesting that 1 as a bicyclic compound.Two of the nonhydrogenated saturated carbons, δ C 74.2 and 72.1, were shifted to high frequency indicating they were attached to oxygen atoms.The EIMS spectrum did not present the molecular ion, but showed ions at m/z 220 (M -H 2 O) and 202 (M -2H 2 O), in agreement with the presence of two hydroxyl groups for 1.The 1 H NMR spectrum indicated resonances corresponding to four methyl groups, three of which were attached to carbons bearing hydroxyl groups: δ H 1.09 (s), 1.19 (s) and 1.20 (s), while the third one (δ H 1.64, s) due to the high frequency chemical shift seemed to be attached to a double bond.The presence of just one olefinic hydrogen δ H 6.14 (br s), suggested the presence of a trisubstituted double bond which is in accordance with 13 C NMR data.
The cis relative configuration for the double bond moieties was supported from the chemical shift at δ 1.11 corresponding to the angular methyl (CH 3 -16) 5 .The proposed stereochemistry was also supported by the NOESY experiment (Figure 2), that showed correlation between H-5β, 3H-16 and H-7.Thus, 2 was identified as 6-ethenyl-5,6,7,8-tetrahydro-6-methyl-7-(1-methylethenyl)-1,4-naphthalenedione.These data were similar to those reported for α-cadinol 16 .Except for the observed differences, especially for the carbon atoms at δ C 53.0 (C-7), 74.2 (C-11), 24.1 (C-12) and 32.1 (C-13), of 1 in respect to those of α-cadinol, what could be explained by the existence of an additional C-11 hydroxyl group in 1.The slight difference between the chemical shift of methyls C-12 and C-13 (δ C 24.1 and 32.1, respectively) revealed that there is no free rotation around the single bond C 7 -C 11 , as expected.From the NOESY data it was possible to assign unambiguously the chemical shift of both carbons through the dipolar interaction of H-6 (δ H 1.93) with the slightly more protected H-12 (δ H 1.19) and the equatorial H-8 (δ H 1.75) with the other one H-13 (δ H 1.20).HMQC data it was easy to assign both carbon chemical shifts.
The relative stereochemistry of 1 was determined by analysis of the NOESY spectrum.The observed nOes for H-1α, H-2α, H-9α and H-7α; for H-6β, H-2β and 3H-14β were consistent with a trans configuration of the A/B rings.These data also suggested that the configurations of HO-10 and HO(CH 3 ) 2 C-7 groups were α and β, respectively (Figure 1).Based on these data, the structure of 1 was determined as the 10α,11-dihydroxy-4-cadinene, which is a new sesquiterpene.
Compound 2 was obtained as an orange oil, and its molecular formula, C 16 H 18 O 2 , was suggested by 13

General experimental procedures
Melting points were determined using a melting point apparatus and are uncorrected.IR spectra were obtained on a Perkin-Elmer 1000 FT-IR instrument.EIMS data were obtained using a VG-Auto Spec mass spectrometer.Optical rotations were measured in a Perkin-Elmer 341 digital polarimeter.The NMR spectra were recorded in a Bruker DRX 500 [500 MHz ( 1 H) and 125 MHz ( 13 C)] spectrometer.Chemical shifts were recorded in δ (ppm) from TMS relative to the solvent absorption relative to TMS, CDCl 3 δ (7.24 and 77.0 ppm), and DMSO-d 6 (2.49 and 39.5 ppm).Column chromatography (CC) was performed using silica gel 60 (Merck).TLC analysis were performed on precoated silica gel UV 254 plates (Aldrich).Visualization of TLC plates was performed using a mixture of vanillin-perchloric acid-EtOH as a spray reagent.Spots were visualized by spraying the plates and then heating them at 100 °C for 1-3 min in a oven.

Plant material
Cordia trichotoma was collected in March 1998, at the Meruoca mountain, State of Ceará, Brazil, and identified by A. S. Nogueira de Castro and E. P. Nunes, botanists of the Universidade Federal do Ceará, where a voucher specimen is deposited (Herbarium Prisco Bezerra, N o .25.165).