Determination of the Absolute Configuration of the Pseudo‐Symmetric Natural Product Elatenyne by the Crystalline Sponge Method

Abstract

Elatenyne is a marine natural product that was isolated in 1986. Despite its simple 2,2′‐bifuranyl backbone, its relative structure was only recently determined. The absolute configuration of elatenyne has still not been unequivocally confirmed because of its pseudo‐meso core structure, which results in a specific rotation, [α]D , of almost zero. In this work, the structure of natural elatenyne was determined by the crystalline sponge method and the use of a porous coordination network (a crystalline sponge) capable of absorbing organic guests; in the sponge, the absorbed guests are ordered and crystallographically observable. The crystalline sponge could differentiate between the two very similar alkyl side chains, and the absolute structure of elatenyne was thus reliably determined. The total amount required for the experiments was only approximately 100 μg, and the majority (95 μg) could be recovered after the experiments.

Racemic and Enantiopure Camphene and Pinene Studied by the Crystalline Sponge Method

“…Others observed that enantiopure compounds can be ordered inside the host channels and give rise to loss of inversion symmetry, possibly aided by solvents. 2 , 22 , 25 − 27 This is indeed the case for β-pinene but we did not observe this for camphene and α-pinene. It is not clear if ordering of enantiopure compounds or of enantiomeric pairs is most common.…”

“…The porous framework introduced by Fujita and responsible for most of the crystalline sponge applications up to now has a space group that in principle is incompatible with chiral compounds. Nevertheless, successful structure determinations of several chiral compounds have been reported, 2 , 25 − 27 but only after guest ordering resulted in the breaking of the inversion/mirror symmetry of the host–guest system. Such symmetry breaking will not always occur, and the problems encountered during the determination of the chirality of miyakosyne A 1 demonstrate that the interplay between chiral guests and the nonchiral host is not yet sufficiently understood.…”

Structure determination of terpenes by the crystalline sponge method

“…These interactions include π-π, CH-π, and charge-transfer interactions. The technique was first introduced by Fujita et al [1] in 2013 and since then has grown rapidly and proven helpful in the structure elucidation of natural products [2], [3] volatile compounds [4], [5], ozonides [6], metabolites [7], in studying reaction mechanisms [8], [9] and in absolute structure determination [10], [11]. With the success of the crystalline sponge method many researchers developed alternative crystalline sponges [12], [13].…”

Natural Products as a Foundation for Drug Discovery

“…Moreover, the Fujita group has updated the methodology (Hoshino, Khutia, Xing, Inokuma, & Fujita, ). To date, most of the applications of this method to characterizing natural‐product structures were performed by the Fujita laboratory (Brkljaca et al., ; Kai, Sogame, Sakurai, Nasu, & Fujita, ; Lee, Hoshino, Fujita, & Urban, ; Matsuda et al., ; Urban, Brkljaca, Hoshino, Lee, & Fujita, ; Yoshioka, Inokuma, Hoshino, Sato, & Fujita, ), although another group has published the absolute configuration determination of a plant metabolite, asarinin, using crystalline‐sponge methods (Li, Yang, Gu, & Di, ). It has been reported that crystalline sponges could be used as an affinity matrix to trap sesquiterpenes from a crude red algal extract for analysis (Wada et al., ).…”