From the CHCl3 extract of the aerial parts of Ononis natrix, a new annual product, N-arachidylanthranilic acid [1] has been isolated, in addition to the known compounds, gardenin B, xanthomicrol, hymenoxin, 8-hydroxy-6-methoxy-3-undecyl-3,4-dihydroisocoumarin, and medicarpin-β-D-glucoside. The structure of 1 was established by spectroscopic and chemical methods. The genus Ononis belongs to the family Leguminosae (tribe Trifoleae) and comprises more than 75 annual or perennial species, indigenous to Eurasia, especially the Mediterranean region (1,2). Ononis natrix L. is a perennial herb distributed throughout Jordan (1,3). Infusions of the roots and flowers of O. natrix have been used for the treatment of certain disturbances of the urinary tract and have been reported to have diuretic and antirheumatic properties (4). Compounds isolated from the genus Ononis have also shown antibiotic and molluscicidal activities (5). The genus Ononis is known to produce triterpenoids (2), anthranilic acid derivatives (5), resorcinol derivatives (4-6), dihydroisocoumarins (4,7), a homopterocarpin (7), aromatic lactones (8), flavonoids, and isoflavonoids (5,6). In this paper we describe the isolation and determination of the structure of a new product, namely, N-arachidylanthranilic acid [1]. From the CHCl3 extract of the aerial parts of Ononis natrix, five known compounds were isolated, namely, gardenin B, xanthomicrol, hymenoxin, 8-hydroxy-6-methoxy-3-undecyl-3,4-dihydroisocoumarin, and medicarpin-β-D-glucoside, which were identified by direct comparison with authentic samples and/or with reported physical and spectral data (4, 9-14). In addition, the novel N-arachidylanthranilic acid [1] was isolated. This is the first report of the isolation of gardenin B, xanthomicrol, hymenoxin, and medicarpin-β-D-glucoside from this genus. Xanthomicrol has shown antispasmodic activity by inhibition of the jejunum in test animals (11), and antimicrobial activity against Aspergillus parasiticus, Candida tropicalis, and Fusarium solani (15). Hymenoxin was found to be cytotoxic to cultured human cells (13). Medicarpin-β-D-glucoside has been previously isolated from the roots of alfalfa (Medicago sativa L.) (14,16), but the 13C NMR data of this substance are reported here for the first time. The structure of 1 was assigned through interpretation of its spectroscopic properties. The 1H-NMR spectrum showed signals due to a system of four vicinal aromatic protons at δ 8.77 (dd, J3,4=8 Hz, J6,4=2 Hz, H-6), 7.60 (ddd, J4,3=8 Hz, J4,5=7 Hz, J4,6=2 Hz, H-4), 7.11 (ddd, J5,6=8 Hz, J5,4=7 Hz, J5,3=2 Hz, H-5), 8.13 (dd, J6,5=8 Hz, J3,5=2 Hz, H-3), together with 32 aliphatic protons appearing between δ 1.24-1.42. In addition, two protons appearing as a triplet at δ 2.47 were assigned to those α- to the amide; the two protons which appeared as a quartet at δ 1.77 were assigned to those positioned β- to the amide. The triplet at δ 0.88 (J=7 Hz) was assigned to the terminal methyl group, and a proton of a secondary amide, which appeared at low field as a broad singlet, was observed at δ 10.93 (5,17). The couplings in the 1H-NMR spectrum of 1 were confirmed by COSY NMR experiments. The methylated derivative 2 showed a similar 1H-NMR spectrum to that of 1, with the only difference being the singlet signal at δ 3.90 due to the methyl ester of an aromatic acid group. A molecular formula of C28H45O3N deduced from the MS for 1 was suggested by the molecular ion at m/z 431, and the number of carbons was confirmed by the 13C-NMR spectrum with the aid of HETCOR NMR experiments. The base peak of compound 1 appeared at m/z 137, corresponding to free anthranilic acid. This can be interpreted as a result of a McLafferty transposition of an aromatic amide after the loss of an alkylketene from the fragment ion at m/z 179 (5,17), and the base peak of the methyl derivative 2 appeared at m/z 151, corresponding to methyl anthranilate. The IR spectrum of 1 showed strong absorptions of the ortho disubstituted benzene ring (1608, 1590, 1455, 755 cm-1), the amide group (3350, 1676, 1535 cm-1), and the aromatic acid (1705, 1418 cm-1) (5,17). Its UV spectrum showed strong absorptions at 253 and 303 nm, consistent with compound 1 being an anthranilic acid derivative (5). With these data and through comparison with those reported for N-13-docosenoylanthranilic acid (5) and for N-docosenoylanthranilic acid (17), we propose the structure of N-arachidylanthranilic acid (N-eicosenoylanthranilic acid) for compound 1.