Glycosylation of cardenolides. VIII. Structures of the by-products of the synthesis by the orthoester method of strophanthidol rhamnosides
The by-products formed in the preparation of strophanthiodol 19-rhamnoside and 3, 19-bisrhamnoside by the orthoester method are 3β,5-dihydroxy-8,19-epoxy-5β,14β, 17α-card-20(22)-enolide and its 3-α-L-rhamnoside. 3β,5-Dihydroxy-8,19-epoxy-5β, 14α,17β-card-20(22)-enolide has been obtained by the action of a solution of HBr in nitromethane on strophanthidol.
Untersuchungen über Steroide XLII. Umwandlung des 17α‐Pseudostrophanthidins in 19‐Hydroxy‐8, 19‐epoxy‐14β, 17α‐cortexon und 8‐Hydroxy‐19‐nor‐14β, 17α‐cortexon
The synthesis of a structural isomer of aldosterone, viz. 19-hydroxy-8, 19-epoxy-(11-) de(s)oxycorticosterone (= 19-hydroxy-8, 19-epoxy-cortexone), and a number of related compounds was reported earlier from this laboratory [1]. It appeared desirable to prepare the corresponding compounds of the 17α-series also, such as 19-hydroxy-8, 19-epoxy-14 β, 17 (βH)-deoxycorticosterone (28). 17 α-Pseudostrophanthidin (2), which has not yet been described in the literature, was considered as starting material for the synthesis of 28. 2 has now been prepared by heating a solution of pseudostrophanthidin (1) in dimethylformamide in the presence of sodium p-toluenesulfonate and anhydrous sodium acetate. 2 was characterized as the 3, 19-diacetate (7), the 19-methylal (8) and the 3-monoacetat (9). 9 was also obtained by acetylating the methylal 8 and demethylating the resulting reaction product 10. To support the structures assigned to 9 and, by implication, to 2, a series of further reactions were carried out.
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.