Influence of conformational factors on acid‐catalyzed cyclizations of germacranolides: Molecular structure of the cyclization products of gallicin and 8α‐hydroxygallicin (shonachalin a)

Abstract

Acid-catalyzed cyclization of the natural germacranolide gallicin (8) yielded, among other products, the l,.l-epoxyeudesmanolide 9, which has a trans-fused decaline system. Under the same conditions the closely related germacranolide shonachalin A (8a-hydroxygallicin) (3) cyclized to the eudesmanolide 4 with a cis-fused decaline system. The structures of these cyclization products were secured by means of chemical correlations and X-ray diffraction analyses.

Acid‐Induced Rearrangement of Epoxygermacra‐8,12‐olides: Synthesis and Absolute Configuration of Guaiane and Eudesmane Derivatives from Artemisiifolin

“…The studied acid‐catalyzed cyclizations of epoxygermacrane follow the well‐established rule that 1,10‐epoxygermacranolides cyclize into eudesmanolides33,34 under acid catalysis, whereas 4,5‐epoxygermacranolides yield guainolides,35 but interesting information concerning the stereochemistry of the epoxides and the presence of substituents can be deducted.…”

Germacrone Derivatives as new Insecticidal and Acaricidal Compounds: A Structure-Activity Relationship

“…The ability of the ten-membered ring of the germacradiene species to undergo conformational changes is well known, and has been the subject of multiple computational studies [14,15,16,17,18,19]. This conformational flexibility plays an important role in their biosynthetic transformation to other sesquiterpene skeletons [20,21], and in the reactivity of these compounds, since the spatial disposition of the different conformers determines the outcome of the corresponding reactions [22,23].…”

Mechanistic investigations on six bacterial terpene cyclases

“…Germacranes have been suggested as general precursors for eudesmanes [56]. Their interconversion could be a non-enzymatic process catalysed by weak acids, e.g., during work-up, but the acid-catalysed conversion of 4a is known to give a mixture of α-, β-, and γ-eudesmol [57], but not 7- epi -α-eudesmol, which demonstrates the participation of the enzyme to fix 4a in the correct conformation for its cyclisation to 4 .…”