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

Nicholas J Sadgrove,Ben-Erik Van Wyk,Ben W Greatrex,Haytham Senbill

doi:10.3390/antibiotics9040173

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.

Highlights

Southern African Widdringtonia were once prized for their timbers and have been heavily exploited over the course of more than a century
The most pronounced impact has been on the critically endangered W. wallichii Endl. ex Carrière (=W. cedarbergensis J.A.Marsh) [1], which was favoured for its durable fragrant timber [2,3]
It was demonstrated that these diterpenes are not restricted to leaves, as they are present in twigs and timber from young thin branches

Summary

Introduction

Southern African Widdringtonia were once prized for their timbers and have been heavily exploited over the course of more than a century. The most pronounced impact has been on the critically endangered W. wallichii Endl. Ex Carrière (=W. cedarbergensis J.A.Marsh) [1], which was favoured for its durable fragrant timber [2,3]. Unlike other species in the genus, it does not re-sprout after fire [3,4]. ‘five’species speciesthat thatare are endemic to South. Africa [5], but, due to taxonomic revisions, the earlier five [6]. Have been reduced endemic to South Africa [5], but, due to taxonomic revisions, the earlier five [6] have been reducedto to three. Today today it it is is unclear unclear which which species species were were examined examined since since the the provenances provenances of of their collections were not recorded

Methods

Results

Conclusion