Early diagenesis of triterpenoids derived from mangroves in a subtropical estuary
Leaves from three mangrove species, and surface and deeper soils along salinity gradients in the Shark River estuary, USA, were analyzed to determine numerous diagenetic degradation products and pathways for mangrove derived triterpenoids. The dehydration of pentacyclic triterpenols was observed in mangrove leaves, leading to pentacyclic triterpadienes with Δ2,12 and Δ2,14 unsaturations. Surprisingly, various mono-unsaturated triterpenes (with Δ12 and Δ14), nor-, bisnor- (24,25-bisnortaraxer-14-ene), trisnor-triterpenes (1,2,3-trisnortaraxera-5(10),14-diene and 1,2,3-trisnortaraxer-14-ene) and tetrakisnor- and pentakisnor-triterpenes were detected in Rhizophora mangle leaves, suggesting that reduction and later demethylation of triterpadienes can occur prior to mangrove leaf abscission or senescence/death. Most of the unsaturated and nortriterpenes were also found in mangrove stand soils (>100 years old), suggesting their relative stability. In addition, a high diversity of aliphatic and aromatic des-A-triterpenes from the taraxerane, oleanane, ursane, and lupane precursors were present in the surface and deeper soils of mangrove stands, suggesting that isomerization, rapid diagenetic loss of ring-A and further aromatization of triterpenoids occurred early during litter decay. The overall diagenetic transformations could be caused by a combination of photodegradation, microbial alteration (bacteria/fungi), anaerobic alteration (reduction), oxidation and secondary processes. Possible mechanisms of the early diagenesis of triterpenoids were proposed using taraxerol, a triterpenol, highly enriched in R. mangle, as an example. These results, coupled with the detection of various intermediate compounds, provide a better understanding of the diagenetic fate of mangrove derived triterpenoids.
He, Ding; Simoneit, Bernd R.T.; Cloutier, Joshua B.; and Jaffe, Rudolf, "Early diagenesis of triterpenoids derived from mangroves in a subtropical estuary" (2018). FCE LTER Journal Articles. 512.
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