ABSTRACT
The chlorohydroquinone tetramer, russuphelol, does not have stereocenters; however, it was reported as a chiral optically active substance with stable enantiomeric conformations. The natural product is synthesized in six steps and 14% overall yield. Synthetic material was used to experimentally investigate its chiral properties.
Subject(s)
Hydrocarbons, Chlorinated/chemical synthesis , Hydroquinones/chemical synthesis , Hydrocarbons, Chlorinated/chemistry , Hydroquinones/chemistry , Molecular Conformation , Molecular Structure , StereoisomerismABSTRACT
Restricted rotations of chemical bonds can lead to the presence of persistent conformational chirality in molecules lacking stereocenters. We report the development of first-of-a-kind predictive rules that enable identification of conformational chirality and prediction of racemization barriers in the diarylether heptanoid (DAEH) natural products that do not possess stereocenters. These empirical rules-of-thumb are based on quantum mechanical computations (SCS-MP2/∞//B3LYP/6-31G*/PCM) of racemization barriers of four representative DAEHs. Specifically, the local symmetry of ring B and the E/Z configuration of the vinylogous acid/ester are critical in determining conformational chirality in the DAEH natural product family.
Subject(s)
Biological Products/chemistry , Ethers, Cyclic/chemistry , Molecular Conformation , Diarylheptanoids/chemistry , Hydrogen Bonding , Kinetics , Stereoisomerism , ThermodynamicsABSTRACT
The first enantioselective Ullmann cross-coupling reactions to prepare diaryl ethers are reported. The reactions were used to prepare the diarylether heptanoid natural products (-)-myricatomentogenin, (-)-jugcathanin, (+)-galeon, and (+)-pterocarine.
Subject(s)
Biological Products/chemical synthesis , Diarylheptanoids/chemical synthesis , Biological Products/chemistry , Diarylheptanoids/chemistry , Molecular Structure , StereoisomerismABSTRACT
The synthesis of the garuganin and garugamblin diarylether heptanoids using an intramolecular Ullmann coupling is reported. Alkene stereoisomers, vinylogous ester regioisomers, and ß-diketone congeners are also synthesized. The chiral properties and free energies of activation for racemization of the garuganin and garugamblin diarylether heptanoids and congeners are determined using dynamic NMR methods. A combination of techniques including coalescence measurements, line shape analysis, and selective inversion experiments are used to measure racemization barriers. None of the garuganin or garugamblin diarylether heptanoids are chiral, despite their reported specific rotation values.
Subject(s)
Diarylheptanoids/chemistry , Diarylheptanoids/chemical synthesis , Magnetic Resonance Spectroscopy , Molecular StructureABSTRACT
The syntheses of myricatomentogenin, jugcathanin, galeon, pterocarine, and acerogenin L are reported. Synthetic material was used to measure their optical activities and free energy of activation for racemization. The natural enantiomers of myricatomentogenin, jugcathanin, galeon, and pterocarine were determined to have the same pR absolute stereochemistry. Acerogenins L and C are achiral compounds.
