New Labdanes with Antimicrobial and Acaricidal Activity: Terpenes of Callitris and Widdringtonia (Cupressaceae)

Abstract

In spite of the evidence for antimicrobial and acaricidal effects in ethnobotanical reports of Callitris and Widdringtonia, the diterpene acids from Widdringtonia have never been described and no comparison to the Australian clade sister genus Callitris has been made. The critically endangered South African Clanwilliam cedar, Widdringtonia wallichii (syn. W. cedarbergensis), of the Cederberg Mountains was once prized for its enduring fragrant timbers and an essential oil that gives an aroma comparable to better known Mediterranean cedars, predominantly comprised by widdrol, cedrol, and thujopsene. In South Africa, two other ‘cedars’ are known, which are called W. nodiflora and W. schwarzii, but, until now, their chemical similarity to W. wallichii has not been investigated. Much like Widdringtonia, Callitris was once prized for its termite resistant timbers and an ‘earthy’ essential oil, but predominantly guaiol. The current study demonstrates that the essential oils were similar across all three species of Widdringtonia and two known non-volatile diterpene acids were identified in leaves: the pimaradiene sandaracopimaric acid (1) and the labdane Z-communic acid (2) with a lower yield of the E-isomer (3). Additionally, in the leaves of the three species, the structures of five new antimicrobial labdanes were assigned: 12-hydroxy-8R,17-epoxy-isocommunic acid (4), 8S-formyl-isocommunic acid (5), 8R,17-epoxy-isocommunic acid (6), 8R-17R-epoxy-E-communic acid (7), and 8R-17-epoxy-E-communic acid (8). Australian Callitris columellaris (syn. C. glaucophylla) also produced 1 and its isomer isopimaric acid, pisiferal (9), and pisiferic acid (10) from its leaves. Callitris endlicheri (Parl.) F.M.Bailey yielded isoozic acid (11) as the only major diterpene. Diterpenes 4–6, pisiferic acid (10), spathulenol, and guaiol (12) demonstrated antimicrobial and acaricidal activity.

New Insights into Antibacterial Compounds: From Synthesis and Discovery to Molecular Mechanisms of Action

“…Results from this study corroborate the traditional use of extracts of Erythrina as antimicrobials by demonstrating the antimicrobial activity of isoflavone derivatives as the active principles [12]. In another paper from Sadgrove et al, the antimicrobial and acaricidal activities of terpenes isolated from Callitris and Widdringtonia (Cupressaceae) were studied [13]. The authors describe, for the first time, new diterpene acids from Widdringtonia and compare their chemistry with that of the genus Callitris from the Australian clade sister [13].…”

“…In another paper from Sadgrove et al, the antimicrobial and acaricidal activities of terpenes isolated from Callitris and Widdringtonia (Cupressaceae) were studied [13]. The authors describe, for the first time, new diterpene acids from Widdringtonia and compare their chemistry with that of the genus Callitris from the Australian clade sister [13]. The paper from Cudalbeanu et al is the first report of the antifungal, antitumoral and antioxidant properties of the Danube Delta Nymphaea alba methanolic extracts [14].…”

Purely Australian Essential Oils Past and Present: Chemical Diversity, Authenticity, Bioactivity, and Commercial Value

“…In later years the plantation was accessed for the blue essential oil, which is used today in aesthetics. A possible dermatological application may involve inhibition of Demodex [32], which is a human ectoparasite that causes skin complaints in some individuals [33].…”

“…Although there are 20 or so accepted species of Callitris, there are four that are known widely in Australia [32,118]. Two of these major species are C. endlicheri (Parl.)…”

“…& L.A.S.Johnson and C. intratropica R.T.Baker & H.G.Sm. are currently regarded as synonyms of C. columnellaris, yet they stand out as distinct chemical entities in chemophenetic analysis [32]. Today they are tentatively regarded as chemotypes before an international audience but are regarded as distinct species within Australia.…”