Germacrene D Cyclization: An Ab Initio Investigation

Abstract

Essential oils that contain large concentrations of germacrene D are typically accompanied by cadinane sesquiterpenoids. The acid-catalyzed cyclization of germacrene D to give cadinane and selinane sesquiterpenes has been computationally investigated using both density functional (B3LYP/6-31G*) and post Hartree-Fock (MP2/6-31G**) ab initio methods. The calculated energies are in general agreement with experimentally observed product distributions, both from acid-catalyzed cyclizations as well as distribution of the compounds in essential oils.

Chemical compositions of the essential oil and calculation the biophysicochemical coefficients of the components of Hymenocrater longiflorus Benth. of Iran

“…In addition, γ-cadinene is more abundant in these essential oils than α-cadinene. α-Cadinene has been shown to undergo acid-catalyzed rearrangement to give β-cadinene [16,30], which in turn, has been found to isomerize to ω-cadinene [16,[30][31][32], in agreement with the calculated energies; β-cadinene and ω-cadinene are lower in energy than α-cadinene by 1.88 kcal/mole and 2.90 kcal/mol, respectively. Bülow and König [16,24] reported that ω-cadinene can be formed from δ-cadinene in a 1.4:1 ratio, consistent with the nearly equal calculated energies.…”

“…The acid-catalyzed cyclization of Germacrene-D to give cadinane and selinane sesquiterpenes has been computationally investigated using both density functional (B3LYP/6-31G*) and post Hartree-Fock (MP2/6-31G**) ab initio methods by Setzer in 2008 [16]. It is generally observed that essential oils containing large concentrations of the sesquiterpene germacrene D are typically accompanied by cadinane and muurolane sesquiterpenoids [16][17][18][19][20][21][22] and germacrene-D has been suggested to serve as biogenetic precursor to a number of different sesquiterpenoid skeletons [16,23,24].…”

“…It is generally observed that essential oils containing large concentrations of the sesquiterpene germacrene D are typically accompanied by cadinane and muurolane sesquiterpenoids [16][17][18][19][20][21][22] and germacrene-D has been suggested to serve as biogenetic precursor to a number of different sesquiterpenoid skeletons [16,23,24]. Bülow and König have demonstrated that germacrene-D readily undergoes acid-catalyzed cyclization to give cadinane, muurolane, and amorphane sesquiterpenes [16,25].…”

“…Bülow and König have demonstrated that germacrene-D readily undergoes acid-catalyzed cyclization to give cadinane, muurolane, and amorphane sesquiterpenes [16,25]. In addition, there is concern that skeletal rearrangements may occur during the hydrodistillation of plant materials to obtain essential oils [16,[26][27][28][29]. Bülow and König [16,24] had found that acid-catalyzed cyclizations of germacrene D generally give a preponderance of δ-cadinene, followed by γ-cadinene, and lesser amounts of α-cadinene.…”

“…In addition, there is concern that skeletal rearrangements may occur during the hydrodistillation of plant materials to obtain essential oils [16,[26][27][28][29]. Bülow and König [16,24] had found that acid-catalyzed cyclizations of germacrene D generally give a preponderance of δ-cadinene, followed by γ-cadinene, and lesser amounts of α-cadinene. The abundant δ-cadinene is consistent with the ab initio calculations, but the calculated energies of α-cadinene and γ-cadinene are not in agreement with the experimental results, and would predict α-cadinene to be more abundant than γ-cadinene.…”