Abstract 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.

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亚热带河口红树林三萜类化合物的早期成岩作用

摘要 分析了美国鲨鱼河河口三种红树林物种的叶子以及沿盐度梯度的表层和深层土壤，以确定红树林衍生的三萜类化合物的多种成岩降解产物和途径。在红树林叶子中观察到五环三萜醇的脱水，导致具有 Δ2,12 和 Δ2,14 不饱和度的五环三萜烯。令人惊讶的是，各种单不饱和三萜（具有 Δ12 和 Δ14）、nor-、bisnor-（24,25-bisnortaraxer-14-ene）、trisnor-triterpenes（1,2,3-trisnortaraxera-5(10),14-在红树林叶片中检测到二烯和 1,2,3-trisnortaraxer-14-ene) 以及四萜和五萜三萜，这表明在红树林叶片脱落或衰老/死亡之前，三萜的还原和随后的去甲基化可能发生。大多数不饱和和去甲三萜也在红树林林分土壤（> 100 年历史）中发现，表明它们相对稳定。此外，来自蒲公英、齐墩果烷、熊果烷和羽扇豆烷前体的脂肪族和芳香族 des-A-三萜存在于红树林的表层和深层土壤中，表明存在异构化、环 A 和环的快速成岩损失。三萜类化合物的进一步芳构化发生在凋落物腐烂的早期。整体成岩转变可能是由光降解、微生物改变（细菌/真菌）、厌氧改变（还原）、氧化和二次过程共同引起的。以蒲公英醇为例，提出了三萜类化合物早期成岩作用的可能机制。这些结果，