Miscellaneous Diterpenes from the Aerial Parts of Plectranthus ornatus Codd

Fábio Nascimento Ávila ,Nairley Cardoso-Sá,Edilberto R Silveira ,Letı́cia V Costa-Lotufo ,Maria Rose Jane R Albuquerque ,Danilo D Rocha ,Mayron Alves De Vasconcelos ,Maria Conceição M Torres ,Francisco C L Pinto ,Edson Holanda Teixeira ,Thiciana S Sousa ,Otília Deusdênia Loiola Pessoa

doi:10.21577/0103-5053.20160255

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.

Highlights

The 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-tumoral7 and diuretic8 have been demonstrated for several isolated compounds from Plectranthus, corroborating with its larger medicinal uses.Plectranthus ornatus Codd
The chromatographic fractionation of the n-hexane extract from the aerial parts of P. ornatus was performed, leading to the isolation of five new diterpenes which were designated as ornatins A-E [1,2,3,4,5], as well as the known diterpenes: coleon R [6],14 ent-3α-hydroxycleroda-4(18), 13E-dien-15-oic acid [7],15 plectrornatin A [8],16 labd‐13‐en8β-hydroxy-15-oic acid [9],17 11-acetoxy-2-oxo-entcleroda-3,13E-dien-15-oic acid [10]18 and ent-11R-acetoxy2-oxocleroda-3,13E-dien-15-oic acid [11]
The 1H and 13C nuclear magnetic resonance (NMR) spectral data (Tables 1 and 2) of 1 were similar to those reported for the diterpenes 11-acetoxyneoclerodane, which were previously isolated of the P. ornatus

Summary

Introduction

The 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-tumoral7 and diuretic8 have been demonstrated for several isolated compounds from Plectranthus, corroborating with its larger medicinal uses.Plectranthus ornatus Codd Colorless resin: [a]D22 −34.44° (c 0.06, CH2Cl2); UV (MeOH) λmax / nm 218; IR (KBr) n / cm-1 3444, 2926, 1694, 1635, 1380, 1235; 1H and 13C NMR (MeOD), see Tables 1 and 2, respectively; HRESIMS m/z, observed: 433.2197; C22H34O7 [M + Na]+ requires 433.2202.

Results

Conclusion