Miscellaneous Diterpenes from the Aerial Parts of Plectranthus ornatus Codd

Abstract

Five new diterpenes derivatives named as ornatin A, B, C, D and E, in addition to six known related diterpenes were isolated from the aerial parts of cultivated specimens of Plectranthus ornatus. The structures were elucidated using a combination of 1D/2D nuclear magnetic resonance (NMR) spectroscopy, high-resolution electrospray ionization mass spectrometry (HRESIMS) and comparison with published NMR data of analogous compounds. All isolated compounds were assayed against four human cancer cell lines, and Gram-positive and Gram-negative bacteria strains. None of them showed any cytotoxic activity, but ornatin C, D, E and three related diterpenes displayed marginal bactericidal or bacteriostatic effects against the Gram-positive strains. Keywords: Plectranthus ornatus, diterpenes, ent-clerodanes, bacteriostatic IntroductionThe genus Plectranthus L'Her (Lamiaceae, subfamily Nepetoideae, tribe Ocimeae, subtribe Plectranthinae) comprises approximately 300 species largely distributed over the African, Asian and Australian continents. 1 Plectranthus is a large genus well known by its diversity of ethnobotanical uses, being especially indicated to treat digestive disorders, skin diseases, infections and respiratory problems. 2 In general, are rich source of essential oils, terpenoids and phenol compounds. 3 Pharmacological properties such as anti-inflammatory, 4 antioxidant, 5 antimicrobial, 6 anti-tumoral 7 and diuretic 8 have been demonstrated for several isolated compounds from Plectranthus, corroborating with its larger medicinal uses.Plectranthus ornatus Codd (syn. Coleus comosus Hochst. ex Gurke) is a perennial and aromatic herb, widespread around the new world. 9 In the northeast of Brazil, P. ornatus, popularly known as "malva santa" or "boldo miúdo", is cultivated as a very important medicinal plant, indicated as analgesic and particularly to treat gastric disorders. 10 Several antimicrobial labdanes, ent-clerodanes, and halimane-type diterpenoids have been previously isolated from P. ornatus. 11 As part of a multidisciplinary program, where the efforts are devoted to study medicinal plants or congeners, in order to unveil their pharmacological or biological properties, herein we describe the isolation and characterization of five new diterpenes derivatives together with six known compounds from the aerial parts of cultivated specimens of P. ornatus, as well as the results of pharmacological and biological assays with the isolated secondary metabolites (Figure 1). Ávila et al. 1015 Vol. 28, No. 6, 2017 Experimental General experimental proceduresOptical rotations were measured on a PerkinElmer 341 digital polarimeter. Infrared (IR) spectra were obtained on a PerkinElmer FT-IR spectrum 1000 spectrometer. Accurate mass spectra were acquired on a liquid chromatography-mass spectrometry ion-trap and time-of-flight (LCMS-IT-TOF, Shimadzu) spectrometer. Nuclear magnetic resonance (NMR) spectra were performed either on Bruker DPX-300 or DRX-500 spectrometers. Open column chromatography (CC) were carried out wit...

Diterpenes Isolated from Three Different Plectranthus Sensu Lato Species and Their Antiproliferative Activities against Gynecological and Glioblastoma Cancer Cells

“…Only a configuration for the C-11 stereogenic center could not be assigned with the NOESY because of the free rotation ability of the side chain. However, based on previous reports − on ent -clerodanes isolated from C. comosus substituted with the same C-9 side chain, the configuration of C-11 was proposed as R *. The E -configuration of the trisubstituted olefinic double bond Δ 13(14) was evident from the characteristic resonances of Me-16 (δ H 2.18, δ C 18.8), ,, and the strong supportive NOE interaction H-12b/H-14 .…”

“…All the ent -clerodanes isolated from C. comosus contain a C-9 side chain with an E -configured Δ 13(14) double bond and a 15-carboxyl group capable of forming methyl esters. − While abietanes 9 – 13 have already been reported to be biosynthesized by C. forsteri “Marginatus” − and are among the most widespread representatives of Plectranthus s.l .…”

“…ex Gürke (syn. Plectranthus comosus, Plectranthus ornatus) was reported to produce spirocoleon- and hydroquinone-type abietanes, , ent -clerodanes, − labdanes, − and halimanes Coleus forsteri“Marginatus” Benth.…”

Diterpenoids from Leaves of Cultivated Plectranthus ornatus

“…Regarding the spasmolytic activity, compounds 1, 4, 5, 7, 11, 12, and 13, including the diterpenes 14 and 15, previously isolated from the n-hexane extract of P. ornatus [28], were assessed for their neurogenic contraction on guinea-pig ileum (▶ Fig. 8).…”

Chemistry of South African Lamiaceae: Structures and Biological Activity of Terpenoids

“…178 exhibited growth inhibitory activity against five Staphylococcus and five Enterococcus strains [75]. Ornatin C, D, E and three related diterpenes displayed marginal bactericidal or bacteriostatic effects against the Gram-positive strains [77]. and 182 showed insect antifeedant activity against Spodopteralittoralis, while 180 showed no antibacterial activity [81,82].…”