Stereochemistry of sesquiterpenes of the germacrane type

Abstract

Among sesquiterpenes, the most common in Nature and the most intensively studied from all-sided stereochemical aspects are the monocyclic germacranes, of which the bicyclic sesquiterpenes eudesmanes, guaianes, carotanes, and others are considered, to be biogenetic derivatives [1, 2].The germacrane skeleton of these natural compounds is based on the carbon skeleton of cyclodecane with two endocyclic double bonds in the 1(10) and 4(5) positions and methyl groups at C4 and C10 and an isopropyl group at C7, in accordance with the isoprene rule. However, examples are found in which one of the double bonds in the germacranolides is shifted into the 9 = 10 position [3], has been replaced by an epoxide group [4], or is absent [5]. Depending on the cis-or transconfigurations of the endocyclic double bonds (or their substituting epoxide groups) in the 1(10) and 4(5) positions of the cyclodecadiene system, they are classified as representatives of four possible geometric isomers [1, 6]:

NMR and x‐ray conformational study of artemisiifolin and three other related germacranolides

“…The combined extracts were dried (Na 2 SO 4 ), filtered and evaporated to dryness, giving a residue (328 mg, 98.6% yield), which was crystallized from EtOAc: m.p. Pyridinium dichromate oxidation of 1: isabelin (3) and compound 4 …”

“…These germacranolides show broadened NMR spectra or even multiple NMR signals indicative of their conformational mobility that causes the existence of two or more conformers in solution at room temperature. 1 -6 In this paper we describe the isolation, structure corroboration and complete conformational analysis by means of 1 H and 13 C NMR spectroscopy and quantum mechanical calculations of the sesquiterpene germacranolides artemisiifolin (1), its 11,13-dihydro derivative (2), isabelin (3) and 6˛-hydroxy-15-oxogermacra-1(10)E,4Z,11(13)-trien-12,8˛-olide (4), and also the x-ray diffraction analysis of 1.…”

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].…”

Natural sesquiterpenoids

“…211 Studies of the conformation of the sesquiterpenes of the germacrane type have been carried out 212 and reviewed. 213 Germacrane D has been identified as the main constituent of the essential oil of the fruits from Smyrnium perfoliatum. 214 Two enantioselective germacrane D synthases have been isolated and characterized from Solidago canadensis, 215 whilst (+)-germacrane A synthase has been obtained from chicory roots (Cichorium intybus).…”