Chemical, molecular and structural studies of Boswellia species: β-Boswellic Aldehyde and 3-epi-11β-Dihydroxy BA as precursors in biosynthesis of boswellic acids.

Ahmed Al-Harrasi,Javid Hussain,Najeeb Ur Rehman,Issa Al-Amri,Abdul Latif Khan,Hidayat Hussain,Muhammed Al-Broumi,René Csuk,David A Lightfoot

doi:10.1371/journal.pone.0198666

Ahmed Al-Harrasi, Javid Hussain + Show 7 more

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https://doi.org/10.1371/journal.pone.0198666

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Abstract

The distribution and biosynthesis of boswellic acids (BAs) is scarce in current literature. Present study aims to elucidate the BAs biosynthetic and its diversity in the resins of Boswellia sacra and Boswellia papyrifera. Results revealed the isolation of new (3β, 11β-dihydroxy BA) and recently known (as new source, β-boswellic aldehyde) precursors from B. sacra resin along with α-amyrin. Following this, a detailed nomenclature of BAs was elucidated. The quantification and distribution of amyrins (3-epi-α-amyrin, β-amyrin and α-amyrin) and BAs in different Boswellia resins showed highest amyrin and BAs in B. sacra as compared with B. serrata and B. papyrifera. Distribution of BAs significantly varied in the resin of B. sacra collected from dry mountains than coastal trees. In B. sacra, high content of α-amyrin was found in the roots but it lacked β-amyrin and BAs. The leaf part showed traces of β-ABA and AKBA but was deficient in amyrins. This was further confirmed by lack of transcript accumulation of amyrin-related biosynthesis gene in leaf part. In contrast, the stem showed presence of all six BAs which are attributed to existence of resin-secretory canals. In conclusion, the boswellic acids are genus-specific chemical constituents for Boswellia species albeit the variation of the amounts among different Boswellia species and grades.

Highlights

Over the centuries, humanity has known and utilized frankincense since ancient times for religious, social and therapeutic purposes [1]
The 1H NMR spectrum of 1 displayed five tertiary methyls, two secondary methyls (δ 0.98, d, J = 6.6 Hz and 0.88, d, J = 6.5 Hz) and a trisubstituted olefinic proton (δ 5.35, d, J = 3.0 Hz), which are characteristic of ursane-type triterpenes related to boswellic acids [52, 53]
The current study showed the isolation and characterization of new chemical constituents from the B. sacra resins along with known αamyrin (3-epi-α-amyrin, β-amyrin and α-amyrin)

Summary

Introduction

Humanity has known and utilized frankincense since ancient times for religious, social and therapeutic purposes [1]. Boswellia sacra Flueck (Burseraceae) is an endemic tree to Oman and an economically important species of genus Boswellia [2, 3]. B. sacra is a good source of high quality frankincense and bioactive compounds having a widerange of vital biological activities. Frankincense exudes from the bark of the tree after a series of man-made incisions about surface area of 10 cm, at a depth of ~5 mm and 6–8 incisions in a season [18]. B. sacra tree is considered one of the economic resources of Oman [24]

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