Structure Determination of 1,3-Dioxolane-Containing Lipids from the Marine Sponge Leucetta sp. Using Chiral 1H NMR Analysis of Model Systems,Journal of Natural Products

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Structure Determination of 1,3-Dioxolane-Containing Lipids from the Marine Sponge Leucetta sp. Using Chiral 1H NMR Analysis of Model Systems
Journal of Natural Products ( IF 3.3 ) Pub Date : 2024-07-17 , DOI: 10.1021/acs.jnatprod.4c00692
A-Young Shin ₁ , Jihoon Lee _{1,

2}

Affiliation

Chemical investigation of n-hexane extract from the marine sponge Leucetta sp. led to the isolation of five new lipids, 1–5, each characterized by a substituted dioxolane core. The structures of 1–5 were established based on the interpretation of NMR and HRESIMS data. To assign the absolute configuration at C-1′, model systems consisting of diastereomers at C-2, C-4, and C-1′ of the dioxolane core were prepared from a chiral glycerol dimethylacetal. ¹H NMR inspection of model compounds revealed that a pair of C-1′ epimers, 11a/c and 11b/d, was indistinguishable, restricting structural assignment by direct comparison of NMR data. In addition, the lack of chromophores in the dioxolane core resulted in unreliable ECD results, with Cotton effects appearing below 190 nm. As an alternative, a chiral NMR method using Eu(hfc)₃ revealed notable lanthanide-induced shifts, allowing the spectroscopic discrimination of 11a/c and ent-11a/c. Therefore, the absolute configuration of all five new lipids was determined to be 2S, 4S, 1′S by direct comparison with the Eu(hfc)₃-induced ¹H NMR data.

中文翻译：

海洋海绵 Leucetta sp 中含 1,3-二氧戊环的脂质的结构测定。使用模型系统的手性 1H NMR 分析

海绵Leucetta sp.正己烷提取物的化学研究。导致分离出五种新脂质1 – 5 ，每种脂质都具有取代的二氧戊环核心。 1 – 5的结构是基于 NMR 和 HRESIMS 数据的解释而建立的。为了确定 C-1' 处的绝对构型，由手性甘油二甲缩醛制备了由二氧戊环核心 C-2、C-4 和 C-1' 处非对映异构体组成的模型系统。模型化合物的¹ H NMR 检查表明，一对 C-1' 差向异构体11a/c和11b/d无法区分，从而限制了通过直接比较 NMR 数据进行的结构归属。此外，二氧戊环核心中缺乏发色团导致 ECD 结果不可靠，在 190 nm 以下出现棉花效应。作为替代方案，使用 Eu(hfc) ₃的手性 NMR 方法揭示了显着的镧系元素引起的位移，从而可以对11a/c和ent- 11a/c进行光谱区分。因此，通过与Eu(hfc) ₃诱导的¹ H NMR数据直接比较，所有五种新脂质的绝对构型被确定为2 S 、4 S 、1 'S 。

更新日期：2024-07-17

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