Synthesis and absolute stereochemistry of marine nor-sesquiterpene austrodoric acid

Further Synthetic Studies Towards the Austrodorane Skeleton: Synthesis of Austrodoral

“…This mixture was then submitted, without purification, to the following key step involving ring contraction in the presence of different acid promoters under different conditions 7–9. By analogy with the synthesis of austrodoric acid ( 2 ),2 we expected that the epoxides 6a and 6b , after opening, would provide the contraction product, aldehyde 1 , however, the secondary alcohol 14 ( a and b enantiomers) was obtained as the main reaction product (Scheme ).…”

“…We used as initial starting material the readily available hydroxy acetate 3 3 (Scheme ). In order to generate the tetrasubstituted double bond between C‐8 and C‐9, we tried to perform a dehydration with iodine in refluxing benzene, using the same conditions as those used for the synthesis of austrodoric acid ( 2 ) 2. However, in this case the dehydration reaction did not occur.…”

“…In order to establish the absolute stereochemistry of these molecules, and also to provide larger amounts of austrodoral ( 1 ) for evaluating its biological activity, we planned synthetic studies towards this carbon framework. The first approach considered in this project led to the formation of austrodoric acid ( 2 ) in nine steps with an overall yield of 8 %, as described recently 2. This synthetic strategy is based on the ring contraction of a suitable homodrimanic epoxide, followed by side‐chain cleavage.…”

Recent Advances in the Syntheses of Decalin Type Natural Products

“…(+)-Austrodoral (138) 56 and (+)-austrodoric acid (139) 57 are two related norsesquiterpenes isolated from the skin extract of Antarctic dorid nudibranch Austrodoris kerguelenensis. They possess a bicyclic structure with the rare carbon skeleton, which could biogenetically arise from a drimane type framework by a ring contraction process.…”

Acid-Promoted Rearrangement of Drimane Type Epoxy Compounds and Their Application in Natural Product Synthesis

“…To confirm the structure of (9S)-31, (9S)-31 was converted to natural (9S)-austrodoric acid (33), as shown in Chart 6. NaBH 4 reduction of (9S)-31 provided a diastereomeric mixture of diols, which was subjected to NaIO 4 12) including the sign of the specific rotation.…”