Salvia polystachya ORT. (Lamiaceae) is a small shrub native from México where its seeds, known as "chía", are used as food and beverage ingredients. 2,3) In Mexican traditional medicine, this plant is mainly used as purgative and antigastralgic, although other uses such as antipyretic, antipaludic, antihemorragic and emollient, have also been described.2) In an earlier work, we isolated eight clerodane type diterpenes (salvifaricin, linearolactone, dehydrokerlin and polystachynes A-E) from this plant.4) Now, we described the isolation of a further clerodane derivative from this species.
Results and DiscussionPolystachyne F (1) was obtained as colorless plates. Its molecular formula, C 20 H 20 O 6 , deduced from the quasimolecular ion peak at m/z 357 (ESI-MS-positive mode), together with the data of the 13 C-NMR DEPT spectrum, revealed its diterpenic nature. The IR spectrum exhibited absorption bands at 1752 (a,b-unsaturated-g-lactone), 1645 (double bonds), 1502 and 874 (b-substituted furan ring) cm
Ϫ1. The 13 C-NMR spectrum confirmed the presence of the g-lactone by the signals of a carboxylic and a oxygenated methylene carbons at d C 172.3 (C-18) and 72.4 (C-19). The latter correlated in the HSQC spectrum with the proton signals of an AB system (Jϭ17.5 Hz) at d H 5.07 (H-19a) and 4.70 (H-19b). 2 J,
3J H-C-couplings of these protons with two non protonated vinylic carbons at d C 126.3 (C-4) and 161.0 (C-5) led to propose a C-4 double bond, whose presence was supported by the allylic couplings between the CH 2 -19 protons and an olefinic proton at d H 6.29 (1H, d, Jϭ11 Hz, H-3), observed in the 1 H-1 H COSY spectrum. In this spectrum, the observed couplings between the H-3 signal and the signal at d H 5.90 (1H, br t, Jϭ8.8 Hz, H-2), and of the latter with that at d H 3.42 (1H, br d, Jϭ5.5 Hz, H-1), which in turn was coupled with the singlet signal at d H 3.01 (1H, H-10), allowed us to established a C-2 double bond and a 1(10) epoxy group. The presence of these functionalities was corroborated by the 13 C-NMR signals at d C 132.9 (C-2), 122.5 (C-3), 57.9 (C-1) and 58.3 (C-10).Clerodane diterpenes usually posses one secondary and one tertiary methyl groups at C-8 and C-9 respectively. In the 1 H-NMR spectrum of 1 only one methyl signal at d H 1.46 (3H, d, Jϭ7.5 Hz) was observed. This signal was assigned to the secondary methyl group (CH 3 -17) at C-8, since the C-8 proton d Analysis of both, Dreiding models and NOESY spectrum of 1 led us to establish its relative configuration as follows: NOE interactions of the equatorial CH 3 -17 with H-7, H-11a and H-12 indicated a 7R, 8S, 9R configurations, if a 12R configuration, as those assigned to the neoclerodanes previously isolated from S. polystachya, 4) is assumed. On the other hand, the b axial H-8 showed strong interactions with H-6, H-7 and H-10, thus establishing a b-orientation of H-10 and, as consequence, a 10R configuration. The NOE between H-2 and H-3 indicated a Z configuration of the C-2 double bond and the NOEs between H-2 and H-10 and between H-1 and H-20 e...