Palmitoleate (=(9Z)‐Hexadeca‐9‐enoate) Esters of Oleanane Triterpenoids from the Golden Flowers of Tagetes erecta: Isolation and Autoxidation Products

Abstract

Six oleanane-type triterpenoid esters were isolated from the golden flowers of Tagetes erecta. Spectral studies characterized their structures as 3-O-[(9Z)-hexadec-9-enoyl]erythrodiol (1), 11a,12a:13b,28-diepoxyoleanan-3b-yl (9Z)-hexadec-9-enoate (2), 13b,28-epoxyolean-11-en-3b-yl (9Z)-hexadec-9-enoate (3), 28-hydroxy-11-oxoolean-12-en-3b-yl (9Z)-hexadec-9-enoate (4), 3-O-[(9Z-hexadec-9-enoyl]-b-amyrin (5), and 11-oxoolean-12-en-3b-yl (9Z)-hexadec-9-enoate (6). Compounds 1 ± 4 and 6 are new natural products, while the known 5 was isolated for the first time from the genus Tagetes, from which only one triterpenoid has earlier been obtained. Aerial oxidation (autoxidation) converted amyrin 1 into 2 ± 4 and transformed amyrin 5 into 6. The configuration of 1 ± 6 and an autoxidation mechanism (Scheme) involving the formation of the intermediate 11a-hydroxyolean-12-ene derivatives 1b and 5b on thermal decomposition of the labile 11a-OOH derivatives 1a and 5a, respectively, under neutral conditions are discussed. For the first time, the reactivity of the allylic HÀC(11) bond of triterpenoids of type 1 and 5 toward aerial oxidation was observed. The long-chain ester group at C(3) of 1 and 5 may be responsible for their labile nature, as b-amyrin (7), erythrodiol (8), and ursolic acid were found to be inert toward autoxidation.

Specific Deuteration in Patuletin and Related Flavonoids via Keto–Enol Tautomerism: Solvent‐ and Temperature‐Dependent 1H‐NMR Studies

“…In quercetin (11), the rate of H/D exchange at C(8) was very high, and HÀC(8) had almost disappeared even at 308; however, in the case of the MeOÀC(6) derivative patuletin (1), the complete exchange occurred at relatively higher temperature (608). It might be due to the negative inductive effect of MeOÀC(6) of 1 which decreases the electron density at C(8), as also revealed by the downfield 13 Table 5). Thus, the absence of MeOÀC(6) is necessary for a greater nucleophilicity at C(8) or for faster keto -enol tautomerism.…”

“…To study the positional effect of OH groups on deuteration of flavonoids, the 1 H-NMR spectra in CF 3 COOD of five flavonols, i.e., galangin (7), kaempferol (8), morin (9), myricetin (10), and quercetin (11), and of three flavones, i.e., apigenin (12), chrysin (13), and luteolin (3) (Fig. 1), were also examined ( Table 6).…”

“…For the individual measurement, the following standard parameters were used: 1 H-NMR, KFID (1 -13) spectral width 5 -7 kHz (1), 7 kHz (1a, 2, and 4), 5.6 kHz (5), 5.7 kHz (6), 8 -10 kHz (11), 6 kHz (9 and 10), 5 kHz (8, 7, 3, and 13), 6 -10 kHz (12). 13 2.2. Reaction Kinetics.…”

“…This regioselectivity and reactivity at C(8) towards deuteration is in agreement with the fact that the nucleophilicity of C (8) is much higher than that of other CH moieties, i.e., HÀC(2'), HÀC(5'), and HÀC(6') in patuletin (1), as supported by its upfield Table 5). Moreover, the 13 C-NMR spectra of 1a did not contain the resonance for the deuterated C(8), due to its increased spin -lattice relaxation time (T 1 ) and also increased complexity and decreased intensity from 13 C,D splitting and a decreased nuclear Overhauser effect [23]. The d(C) of all the undeuterated C-atoms of 1a are similar to those of 1, except for the C-atoms adjacent to C(8), i.e., C(7) and C(8a) which appeared upfield [23] as compared to those of 1 due to deuteration at C (8).…”

Tagetes erecta

“…Lutein esters, α-tocopherol, β-tocopherol, γ-tocopherol and δ-tocopherol were the dominant antioxidant compounds in the fl ower extracts (Gong et al 2011 Six oleanane-type triterpenoid esters were isolated from the golden fl owers of Tagetes erecta , and their structures characterized as 3-O -[(9 Z )-hexadec-9-enoyl]erythrodiol (1), 11 α ,12 α :13 β ,28-diepoxyoleanan-3 β -yl (9 Z )-hexadec-9-enoate (2), 13 β ,28-epoxyolean-11-en-3 β -yl (9 Z )-hexadec-9-enoate (3), 28-hydroxy-11-oxoolean-12-en-3 β -yl (9 Z )-hexadec-9-enoate (4), 3-O -[(9 Z )-hexadec-9-enoyl]-β -amyrin (5) and 11-oxoolean-12-en-3 β -yl (9 Z )-hexadec-9-enoate (6) (Faizi and Naz 2004 ). Aerial oxidation (autoxidation) converted amyrin 1 into 2-4 and transformed amyrin 5 into 6.…”