Identification of new labdane diterpenoids from the aerial parts of Otostegia persica utilizing NMR and circular dichroism calculations

The genus Otostegia (Lamiaceae) encompasses 33 species growing worldwide [1]. The Iran flora, comprises three species of this genus, which are growing in tropical and subtropical regions. In traditional medicine, Otostegia persica is used for the treatment of malaria, headache, diabetes, stomachache, and rheumatoid arthritis, but also to promote wound healing [2],[3]. Phytochemical investigations of a petroleum ether subfraction of O. persica extract resulted in isolation of three new labdane diterpenes with spiro skeleton (1-3) and two derivatives comprising a furan ring (4 and 5). The relative configuration of the isolated compounds was established by analysis of NOESY correlations along with ¹H and ¹³C NMR and DP4+ probability calculations, while the absolute configuration was determined by quantum chemical calculation methods and comparison of calculated and experimentally obtained ECD spectra.

Therefore, the isolated compounds were identified as (2ʹ’S,3R,4a’’S,5R,5ʹR,6ʹ’R,8a’’S)-6ʹ’-hydroxy-5-methoxy-2ʹ’,5ʹ’,5ʹ’,8a’’-tetramethyldecahydro-2H,2ʹ’H-dispiro[furan-3,2ʹ-furan-5ʹ,1ʹ’-naphthalen]-3ʹ’(4ʹ’H)-one (1), (2ʹ’S,3R,4ʹ’S,4a’’S,5R,5ʹR,6ʹ’R,8a’’S)-4ʹ’,6ʹ’-dihydroxy-5-methoxy-2ʹ’,5ʹ’,5ʹ’,8a’’-tramethyldecahydro -2H,2ʹ’H-dispiro[furan-3,2ʹ-furan-5ʹ,1ʹ’-naphthalen]-3ʹ’(4ʹ’H)-one (2), (2ʹ’S,3S,4a’’S,5R,5ʹR,6ʹ’R, 8a’’S)-6ʹ’-hydroxy-5-methoxy-2ʹ’,5ʹ’,5ʹ’,8a’’-tetramethyldecahydro-2H,2ʹ’H-dispiro[furan-3,2ʹ furan-5ʹ,1ʹ’-naphthalene]-2,3ʹ’(4ʹ’H)-dione (3), (4aS,7R,8aR)-4-(2-(furan-3-yl)ethyl)-7-hydroxy-3,4a,8,8-tetramethyl-4a,5,6,7,8,8a-hexahydronaphthalen-2(1H)-one (4), (1S,4aS,7R,8aR)-4-(2-(furan-3-yl)ethyl)-1,7-dihydroxy-3,4a,8,8-tetramethyl-4a,5,6,7,8,8a-hexahydronaphthalen-2(1H)-one (5).

• References

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• 2 Tofighi Z, Alipour F, Hadavinia H, Abdollahi M, Hadjiakhoondi A, Yassa N. Effective antidiabetic and antioxidant fractions of Otostegia persica extract and their constituents. Pharm Biol 2014; 52 , 961-966
• 3 Sadeghi Z, Akaberi M, Valizadeh J. Otostegia persica (Lamiaceae): a review on its ethnopharmacology, phytochemistry, and pharmacology. Avicenna J Phytomed 2014; 4: 79-88