Pinguisane-Type Sesquiterpenes from the South American Liverwort Porella recurva (Taylor) Kuhnemann
The chemical composition of a dichloromethane extract of the South American liverwort Porella recurva has been examined. Two new pinguisane-type norsesquiterpenoid natural products were isolated: 6,11-epoxy-15-nor-3,4-dioxo-5,10-pinguisadien-12-acetate and 6,11- epoxy-15-nor-4-oxo-5,10-pinguisadien-12-acetate. In addition two known pinguisane-type sesquiterpenes were also isolated: norpinguisone and norpinguisone methyl ester. All structures were elucidated by means of NMR spectroscopic techniques and mass spectrometry.
SESQUITERPENOIDS FROM THE LIVERWORT DICRANOLEJEUNEA YOSHINAGANA (Hatt.) Mizut.
A sesquiterpene alcohol with a new rearranged pinguisane carbon skeleton, which is named a neo-pinguisane type, has been isolated from the ether extract of the liverwort Dicranolejeunea yoshinagana (Hatt.) Mizut., together with two new pinguisane-type sesquiterpenoids and previously known deoxopinguisone and ptychanolide. Their structures were established by spectroscopic means.
Diagnosis of the σ-, π- and (σ+π)-Aromaticity by the Shape of the NICSzz-Scan Curves and Symmetry-Based Selection Rules
The NICSzz-scan curves of aromatic organic, inorganic and “all-metal” molecules in conjunction with symmetry-based selection rules provide efficient diagnostic tools of the σ-, π- and/or double (σ + π)-aromaticity. The NICSzz-scan curves of σ-aromatic molecules are symmetric around the z-axis, having half-band widths approximately less than 3 A with the induced diatropic ring current arising from Tx,y-allowed transitions involving exclusively σ-type molecular orbitals. Broad NICSzz-scan curves (half-band width approximately higher than 3 A) characterize double (σ + π)-aromaticity, the chief contribution to the induced diatropic ring current arising from Tx,y-allowed transitions involving both σ- and π-type molecular orbitals. NICSzz-scan curves exhibiting two maxima at a certain distance above and below the molecular plane are typical for (σ + π)-aromatics where the π-diatropic ring current overwhelms the σ-type one. In the absence of any contribution from the σ-diatropic ring current, the NICSzz(0) value is close to zero and the molecule exhibits pure π-aromaticity.