First total synthesis and absolute stereochemical assignment of vittarilide-A, an antioxidant extractive component isolated from Vittaria anguste-elongata Hayata

First Stereoselective Total Synthesis of Marliolide-(4R,5R,3E)-4-hydroxy-5-methyl-3-tetradecylidenedihydrofuran-2(3H)-one and Vittarilide-B: A Unified Strategy Utilizing a Chiral Pool Approach

The first stereoselective total synthesis of the natural products Marliolide-(4R,5R,3E)-4-hydroxy-5-methyl-3-tetradecylidenedihydrofuran-2(3H)-one (1) and Vittarilide-B (1b) has been accomplished using a carbohydrate-based approach starting from d-glucose. The synthesis of Marliolide-(4R,5R,3E)-4-hydroxy-5-methyl-3-tetradecylidenedihydrofuran-2(3H)-one (1) was achieved in 13 steps with an overall yield of 6.5%, featuring key transformations such as reduction, Wittig olefination, TEMPO-mediated oxidation, isomerization, and debenzylation. Vittarilide-B (1b) was synthesized in 18 steps with an overall yield of 8.8%, involving crucial steps like inversion, radical-mediated lactonization, Steglich esterification, and deprotection. The synthesis of Marliolide (1) led to the discovery of a notable isomerization phenomenon, where the Z -isomer was converted to the E -isomer during the oxidation step using BAIB and TEMPO. Various reaction conditions were investigated for this isomerization process, with the TEMPO-mediated reaction consistently providing the best results. The synthesis of Vittarilide-B (1b) required the inversion of stereochemistry at the C-2 position of the common intermediate 6b, followed by a sequence of steps to obtain the final product. The analytical data for both synthetic Marliolide-(4R,5R,3E)-4-hydroxy-5-methyl-3-tetradecylidenedihydrofuran-2(3H)-one (1) and Vittarilide-B (1b) were consistent with the data reported for the natural compounds. This work demonstrates the efficiency of using readily available chiral pool materials like d-glucose in the stereoselective synthesis of complex natural products and provides a foundation for further exploration of their biological activities and potential therapeutic applications.

Semi-synthesis and Structure-Activity Relationship of Neuritogenic Oleanene Derivatives

(3S,4R)-23,28-Dihydroxyolean-12-en-3-yl (2E)-3-(3,4-dihydroxyphenyl)acrylate (1 a), which possesses significant neuritogenic activity, was isolated from the traditional Chinese medicine (TCM) plant, Desmodium sambuense. To confirm the structure and to assess biological activity, we semi-synthesized 1 a from commercially available oleanolic acid. A series of novel 1 a derivatives was then designed and synthesized for a structure-activity relationship (SAR) study. All synthetic derivatives were characterized by analysis of spectral data, and their neuritogenic activities were evaluated in assays with PC12 cells. The SAR results indicate that the number and position of the hydroxy groups on the phenyl ring and the triterpene moiety, as well as the length of the (saturated or unsaturated) alkyl chain that links the phenyl ring with the triterpene critically influence neuritogenic activity. Among all the tested compounds, 1 e [(3S,4R)-23,28-dihydroxyolean-12-en-3-yl (2E)-3-(3,4,5-trihydroxyphenyl)acrylate] was found to be the most potent, inducing significant neurite outgrowth at 1 μm.