Structure of iskenderolide

Abstract

We continued research on the structure of a new sesquiterpene lactone isolated from the aerial part of Artemisia iskenderiana Rzazade, a new sage species described by Rzazade [1] but not recognized by Polyakov [2,3].The composition of iskenderolide was C 15 H 22 O 4 , mp 190-191°C. The IR spectrum showed absorption bands for hydroxyls (3300 cm -1 ), a J-lactone carbonyl (1755), and double bonds (1665, 1650). The appearance in the IR spectrum of a strong band at 910 cm -1 indicated that the molecule might contain a methylene double bond [4].The PMR spectrum of the compound exhibited a doublet for a secondary methyl on a lactone ring (1.42 ppm, J = 7 Hz, CH 3 -CH<) and a singlet characteristic of a vinylmethyl (1.60 ppm). Weakly split (by ~1.5 Hz) 1H doublets at 5.13 and 5.40 ppm belonged to a H 2 C=C< group.The appearance in the spectrum of resonances for exomethylene and vinylmethyl groups in addition to a doublet for an olefinic proton (5.28 ppm, J = 9.65 Hz) suggested that the molecule contained methylene and secondary-tertiary double bonds. A 2H resonance at 3.84 ppm was apparently the result of the overlap of lactone and gem-hydroxyl protons. The gemhydroxyl proton of a second OH group appeared in the spectrum as a triplet at 4.35 ppm (1H, J = 9.65 Hz).According to 13 C NMR, 13 C DEPT 135, 13 C DEPT 90, and 13 C DEPT 45 spectra, iskenderolide was based on a germacrane C skeleton and not guaiane, as proposed earlier [5]. The 13 C NMR spectrum taken with full suppression of proton spin-spin coupling showed 15 singlets (15.0, 17.0, 35.0, 36.0, 42.0, 43.0, 58.0, 72.0, 76.0, 83.0, 112.0, 129.0, 137.0, 152.0, and 180.0 ppm) that were consistent with the presence in the molecule of 15 C atoms. According to 13 C DEPT 45 and 13 C DEPT 135 spectra, 12 of these belonged to protonated C atoms. Of those, the ones at 15.0 and 17.0 were characteristic of two methyls; 35.0, 36.0, and 42.12, three cyclic methylenes; 112.0, an exocyclic methylene; 42.0, 58.0, 72.0, 76.0, and 83.0, five methines; 137.0, an olefinic C atom. Resonances at 138.0, 152.0, and 180.0 ppm in the 13 C NMR spectrum were due to three unprotonated C atoms, i.e., C-10, C-4, and C-12, respectively.Because the resonance of the gem-hydroxyl proton of one OH group overlapped the resonance of the lactone proton (3.84 ppm), the structure of the overlapping resonances could not be examined. Therefore, iskenderolide was acetylated. This produced a compound of formula C 19 H 26 O 6 , mp 142-143°C. Its IR spectrum showed absorption bands for a J-lactone C=O (1790 cm -1 ), ester C=O (1730, 1230), and double bonds (1675, 1650). The PMR spectrum exhibited two 3H singlets (2.01, 2.08 ppm) belonging to two acetyl groups. Now the gem-acetyl protons appeared in the spectrum as a doublet with weakly split (~1.5 Hz) components at 4.65 ppm (1H, J = 9.20 Hz) and a triplet at 5.40 ppm (1H, J = 9.65 Hz). The lactone proton appeared as a 1H multiplet at 3.9 ppm. A doublet at 1.35 ppm (3H, J = 7 Hz, CH 3 -CH<) and a singlet at 1.70 ppm (3H, CH 3 -C=) in the PMR spectrum of diacetyl...

A new esterified furocoumarin from Heracleum pastinacifolium

“…Compound 1 (0.1 g) was dissolved in pyridine (3 mL), treated with acetic anhydride (5 mL), heated on a water bath for 5 h, left at room temperature overnight, and worked up by the known method [6] to afford diacetate C 21 H 20 O 9 , mp 120-122°C.…”

Sesquiterpene lactones in the aerial part of Artemisia maritima L.

“…After a detailed study from a pharmacological point of view, they were proposed for use in medical practice. Ongoing research on the study of sesquiterpene lactones of species of the genus Artemisia L. expands our knowledge on the detection of the substance of the species within the genus [Serkerov et al, 1985;Serkerov, Aleskerova, 1987, 2011.…”