Nasimaluns A and B: neo-Clerodane Diterpenoids from Barringtonia racemosa Choudhury M. Hasan, Shimul Khan, A. Jabbar, and Mohammad A. Rashid* Phytochemical Research Laboratory, Faculty of Pharmacy, University of Dhaka, Dhaka-1000, Bangladesh Received October 1, 1999 An ethanolic extract of the roots of Barringtonia racemosa afforded two novel neo-clerodane-type diterpenoids, methyl-15,16-epoxy-12-oxo-3,13(16),14-neo-clerodatrien-18,19-olide-17-carboxylate (nasi- malun A, 1) and dimethyl-15,16-epoxy-3,13(16),14-neo-clerodatrien-17,18-dicarboxylate (17-carboxy- methylhardwickiic acid methyl ester, nasimalun B, 2) by NMR and MS analyses and by comparison of their spectral data with related compunds. The relative stereochemistry of the asymmetric centers in 1 and 2 was determined by selective 1D NOESY experiments. Barringtonia is an important Old World genus of the family Lecythidaceae and consists of 20 species distributed from tropical Africa to Formosa, Polynesia, and northern Australia. 1 B. racemosa Blume (Bengali name, “Mohaso- mudra”) is an evergreen tree that grows in the Sunderban of Bangladesh, Sri Lanka, and the west coast of India. 2 Several species found in India are used as folk medicines. The seeds are aromatic and useful in colic and opthalmia. 3 Barringtonia species have been shown to contain poly- hydroxylated triterpenoids 1,4 and saponins. 5-7 We have examined B. recemosa, and in this paper we report the structures of two new neo-clerodane diterpenes (1, 2). The concentrated ethanolic extract of B. racemosa was diluted with H 2 O and then extracted with CHCl 3 . Frac- tionation of the CHCl 3 -soluble materials by vacuum liquid chromatography (VLC) and TLC afforded two neo-clerodane diterpenes (1, 2). HRFABMS of compound 1 established its molecular formula as C 21 H 24 O 6 . Its IR spectrum dis- played bands indicating a furan ring (ν 1562, 1507, 873 cm -1 ) and three carbonyl groups (ν 1770, 1730, 1669 cm -1 ). The 1 H and 13 C NMR spectra of 1 closely resembled those of tambalin (3), an insect antifeedant neo-clerodane isolated from Tanacetum balsamita, 8 and bacchasmacranone (4) obtained from Baccharis macraei. 9 Typical low-field signals in the 1 H NMR spectrum of 1 at δ 6.73 (H-14), 7.42 (H-15), and 8.01 (H-16) suggested the presence of a 3-substituted furan ring. The downfield resonance of H-16 revealed that the furan ring was conjugated with a carbonyl group, 10 which was confirmed by the HMBC correlation of H-14 with the ketone carbon at δ C 193.6 (C-12). This structural fragment was identical to that found in 15,16-epoxy-12- oxo-8(17),13(16),14-labdatrien-20,19-olide. 11 The 1 H NMR spectrum of 1 further showed signals for an R,-unsatur- ated 18,19-clerodanolide at δ 6.74 (H-3), 3.93 (H-19a), and 4.33 (H-19b). 9 HMBC correlations from H-3 to C-5 and C-18 and from H-19b to C-4, C-5, C-6, and C-18 confirmed the 18,19-olide functionality in 1. The AB quartet centered at δ 2.83 and 3.04 assignable to H 2 -11 demonstrated connec- tivities over two bonds to δ C 39.6 (C-9) and C-12 and over three bonds to δ C 48.7 (C-8), 46.7 (C-10), and 19.2 (C-20) in the HMBC spectrum. The last correlation placed the single methyl group resonating at δ 0.82 on C-9. The doublet of doublets at δ 3.21 was attributed to H-8, and the HMBC correlation from this proton to the ester carbonyl at δ 174.0 placed the carboxymethyl substituent (δ H 3.60; δ C 51.4) on C-8. It was possible to trace all of the proton-proton spin systems in 1 with data from a COSY-45 experiment. Heteronuclear correlation experiments (HMBC and HMQC) allowed unambiguous assignment of all 1 H and 13 C NMR resonances in 1. The relative stereochemistry of the chiral centers in 1 was determined by selective 1D NOESY experiments. Irradiation at the resonance frequency of H-10 produced significant NOESY correlations with H-1eq, H-6ax, and H-8, while H 3 -20 showed strong NOESY interactions with H-1ax, H-7ax, H 2 -19, and both of the C-11 methylene proton resonances. This established a cis relationship between H-8 and H-10 and between the methyl group at C-9 and H 2 -19. Thus, the side chain at C-9 was assigned the equatorial configuration. The key NOE correlations are depicted on the structure 1. On this basis, the new diterpene was identified as methyl-15,16- epoxy-12-oxo-3,13(16),14-neo-clerodatrien-18,19-olide-17- carboxylate, for which we have proposed the trivial name nasimalun A (1). The molecular formula for 2 was established as C 22 H 30 O 5 from HRFABMS. The 13 C NMR spectrum showed 22 signals, while DEPT and HMQC experiments confirmed that 16 out of the 22 carbons in 2 were attached to protons. The 1 H and 13 C NMR spectral data of 2 were, in part, identical to those reported for hardwickiic acid methyl ester (5), 12 suggesting a close structural similarity between these two compounds. However, resonances appropriate for a secondary methyl group in 5 were absent in the spectra of 2 and were replaced with resonances indicative of a carboxymethyl residue. In fact, the 1 H and 13 C NMR spectra of 2 displayed signals for two carboxymethyl groups, as compared to one in case of hardwickiic acid methyl ester (5). The second carboxymethyl moiety in 2 was placed at C-8 as determined by HMBC experiments. The relative stereochemistry of compound 2 was also established by 1D NOESY experiments as shown. NOESY data established the cis relationship between H-8 and H-10 and between H 3 -19 and H 3 -20. Thus, compound 2 was identified as dimethyl-15,16-epoxy-3,13(16),14-neo-cleroda- trien-17,18-dicarboxylate (17-carboxymethylhardwickiic acid methyl ester, 2) for which the trivial name nasimalun B has been proposed. Experimental Section General Experimental Procedures. Optical rotations were measured on a JASCO DIP-370 polarimeter using a sodium lamp (589 nm). UV and IR spectra were obtained on V-500 UV/VIS (JASCO) and IR-230 (JASCO) spectrophotom- eters, respectively. 1 H NMR spectra were obtained in CDCl3 on a FG 2Hx54 T)25 A600 instrument operating at 600 MHz, * To whom correspondence should be addressed. Present address: SAIC Frederick, NCI-Frederick Cancer Research and Development Center, Bldg. 560, Rm. 32-63B, Post Box B, Frederick, MD 21702. Tel.: (301) 846-1295. Fax: (301) 846-6157. E-mail: rashid@mail.ncifcrf.gov. 410 J. Nat. Prod. 2000, 63, 410-411 10.1021/np990488l CCC: $19.00 © 2000 American Chemical Society and American Society of Pharmacognosy Published on Web 02/12/2000