New Tetranortriterpenoids from Swietenia humilis (original) (raw)

1993, Journal of Natural Products

Abstract

FOU~ new tetranortriterpenoids, humilinolides A Ill, B 127, C 131, and D 147, were isolated from the seeds of Swietenia burnilis (Meliaceae). The structures of compounds 1 4 were established by spectroscopic methods. The structure of humilinolide A 111 was confirmed unequivocally by single crystal X-ray diffraction studies. The effect of the MeOH extract of the seeds and the isolated terpenoids 1 4 on the radicle growth of Amaranth hypochondriacus and Echinochloa m-galli was evaluated. The extract and compounds 1 and 3 caused significant inhibition on radicle elongation in both target species. In addition, the MeOH extract of seeds of S. burnilis showed moderate inhibition to the growth and feeding of the third instar larvae of Tenehio molitw. Swietenia burnilis Zuccarini (Meliaceae), locally known as "topilote," "cobano," "caobilla," and "sopilocuahuilt," is a tree up to 20 m high. It grows commonly in the tropical areas of Mexico, in Guerrero, Michoacan, Colima, Sinaloa, and Chiapas, where the trees are most often seen as scattered and isolated individuals (1,2). The seeds of this plant are highly valued for their medicinal properties in some regions of Mexico (2-5). Decoctions or infusions of the ground seeds are used as anthelmintic agents and for the cure of amebiasis (4). They are also considered effective for treatment of chest pains, coughs, and cancer (5). S. burnilis has recently been listed as an endangered species in need of conservation (1). Previous phytochemical analysis conducted with the seeds led to the isolation and characterization of three tetranortriterpenoids of the mexicanolide group, namely, humilin B, 2-methyl-2-hydroxy-3-isobutyryloxymeliac-8(3O)-enate, and 2-methyl-3tygloyloxymeliac-8(3O)-enate (5). Continuing our search for biologically active substances from Mexican medicinal plants (7,8), we have investigated the seeds ofS. burnilis. In this paper we describe the isolation and structure elucidation of four new tetranortriterpenoids, humilinolides A 111, B 121, C {3], and D {4], as well as their effect on the radicle growth of Amaranthus bypocbondriaws L. and Ecbinocbloa crus-galli (L.) Beauv. The feeding deterrence and growth inhibition of the MeOH extract of dry seeds of S. burnilis on third instar larvae of Tenekio mlitor were also investigated. 'Chemical Studies on Mexican Plants used in Traditional Medicine XXVIII. For part XXVII see M.R.

Figures (5)

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‘ABLE 1. ‘H-nmr Data for Humilinolides A {1}, B {2}, C [3], and D [41 "Chemical shifts (relative to TMS) are in ppm and coupling constants (in parentheses) in Hz. The assignments were made by a combination of COSY and HETCOR. *Overlapped signal.

![BLE 2. °C nmr Data of Humilinolides A {1}, B {2], C [3], and D [4].* spectra of 3 were similar to those of compound 1, except that the signals for the epoxide, the isobutyryl at C-3, the hydroxyl-bearing methine, and the quaternary carbinolic carbon (C-2) were missing. In their place were signals for a trisubstituted olefin (8, 137.52 and 125.52; 8,, 5.37), a tigloyl moiety (6, 166.49, 127.28 and 139.59; 8, 6.93, 1.84 and 1.75), a methylene a to the carboxymethyl group 8, 32.62; 8,, 2.40 (dd), 2.37 (dd)}, and for one quaternary carbon bearing an acetoxy group (8, 169.05, 85.05 and 21.49; 8, 2.14), respectively. The signals due to H-3 (5 5.61) and H-30 (8 5.37) appeared asa sharp and broad singlet, respectively, and were consistent with the presence of a substituent at C-2. In this case H-30 exhibited long range coupling with H-9 and H-14. This long range coupling has been previously described for related compounds possessing a C-8/C-30 double bond (11). The placement of the tigloyloxy and acetoxy

BLE 2. °C nmr Data of Humilinolides A {1}, B {2], C [3], and D [4].* spectra of 3 were similar to those of compound 1, except that the signals for the epoxide, the isobutyryl at C-3, the hydroxyl-bearing methine, and the quaternary carbinolic carbon (C-2) were missing. In their place were signals for a trisubstituted olefin (8, 137.52 and 125.52; 8,, 5.37), a tigloyl moiety (6, 166.49, 127.28 and 139.59; 8, 6.93, 1.84 and 1.75), a methylene a to the carboxymethyl group [8, 32.62; 8,, 2.40 (dd), 2.37 (dd)}, and for one quaternary carbon bearing an acetoxy group (8, 169.05, 85.05 and 21.49; 8, 2.14), respectively. The signals due to H-3 (5 5.61) and H-30 (8 5.37) appeared asa sharp and broad singlet, respectively, and were consistent with the presence of a substituent at C-2. In this case H-30 exhibited long range coupling with H-9 and H-14. This long range coupling has been previously described for related compounds possessing a C-8/C-30 double bond (11). The placement of the tigloyloxy and acetoxy

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groups at C-3 and C-2, respectively, was confirmed by the 'H and °C long range COSY spectrum. The carbonyl C signal at 166.49 (C-24) showed long range correlation not only with the signal at 8 1.84 (H-27) but also with the resonance at 8 5.61 (H-3), in agreement with the tigloyloxy being at C-3. The carbonyl resonance at 8 169.05 correlated with H-3 and H-30, consistent with the presence of the acetoxy unit at C-2. The relative stereochemistry of 3 was determined from the coupling constants of each proton (Table 3) and by the NOESY spectrum; nOe’s were observed between H-29 and H-3, H-5 and H-25; between H-19 and H-6, H-9 and H-28; between H-28 and H-3 and H-19; and between H-18 and H-21, H-22, H-15a, and H-14. Humilinolide D [4] had the composition C,,H;,0,,. Its spectral properties sug-

TABLE 3. Effect of the MeOH Extract of Dry Seeds of Swietenia humilis on the Growth and Food Consumption on the Third Instar Larvae of Tenebrio molitor.”

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References (25)

1. HumilinolideB [2].
2. -White crystals (EtOAc/isopropyl ether); mp 280-282';
3. D -68.5 (2, CHCI,);
4. ir umax (KBr) 3466,1736, 1720-1710,, 1458,1374,1218,875 cm-'; eimsmlz (rel. int.) [MI' 630 (55), 542 (201, 525 (5), 492 (30), 483 (lo), 411 (151, 383 (15), 295 (51, 235 (51, 43 (100). A d . calcd for C3,H4,012: C 62.85, H 6.66; found C 62.90, H 6.59. HumilinolideC [Q].
5. --Crystalline solid (EtOAc/isopropyl ether): mp 21 1-212'; {a]D -55 (2, CHC1,);
6. irumax(KBr) 173C-1710,1430,1370,, 1220,87Ocm-';eimsn/z(rel. int.)[b€l+610(4), 568(16),551
7. --Crystalline solid (EtOAclisopropyl ether); mp 263-264'; [a)D -76.5 (2, CHCI,);
8. ir u max (KBr) 3420, 1740, 1725-1710, 1430, 1375, 1280, 1220,870 cm-'; eims mlz (rel. int.)
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