Syntheses, and Structural and Physical Properties of Axially Chiral Biaryl Dicarboxylic Acids Bearing Chalcogen Atoms.

The preparation, optical resolution, and structural investigations of a series of axially chiral biaryl dicarboxylic acids bearing oxygen, sulfur, and selenium atoms were carried out. The crystal structures of sulfur- and selenium-containing derivatives revealed that the carboxy groups of these compounds are located in a co-planar geometry with the fused aromatic rings including the chalcogen atoms. These conformational controls were found to be achieved by chalcogen-bonding interactions between chalcogen atoms in the aromatic rings and oxygen atoms in the carboxy groups. Even in the case of a binaphthofuran derivative, in which the formation of chalcogen-bonding interactions was expected to be negligible, the carboxy groups were also found to be located in a co-planar geometry toward its fused cyclic rings. Natural bond orbital (NBO) analyses of these dicarboxylic acids indicated the formation not only for the chalcogen-bonding interactions for S and Se derivatives, but also the tetrel-bonding interactions between the oxygen atoms in the carboxy groups and the carbon atoms in the fused cyclic rings for all biaryl dicarboxylic acids. These tetrel-bonding interactions were thought to contribute to conformational control in the binaphthofuran derivative. Physical and chiroptical properties such as the racemization barriers and circular dichroism (CD) spectra of these biaryl dicarboxylic acids were also revealed.

Concise synthesis of catechin probes enabling analysis and imaging of EGCg.

A concise synthesis of APDOEGCg (3) was accomplished. Due to the reactivity of its amine group, the compound could be easily converted to the fluorescein probe 21 and immunogen probe 22 efficiently. We then demonstrated the usefulness of the probes for imaging studies and the generation of antibodies.

Structural characteristics of green tea catechins for formation of protein carbonyl in human serum albumin.

Catechins are polyphenolic antioxidants found in green tea leaves. Recent studies have reported that various polyphenolic compounds, including catechins, cause protein carbonyl formation in proteins via their pro-oxidant actions. In this study, we evaluate the formation of protein carbonyl in human serum albumin (HSA) by tea catechins and investigate the relationship between catechin chemical structure and its pro-oxidant property. To assess the formation of protein carbonyl in HSA, HSA was incubated with four individual catechins under physiological conditions to generate biotin-LC-hydrazide labeled protein carbonyls. Comparison of catechins using Western blotting revealed that the formation of protein carbonyl in HSA was higher for pyrogallol-type catechins than the corresponding catechol-type catechins. In addition, the formation of protein carbonyl was also found to be higher for the catechins having a galloyl group than the corresponding catechins lacking a galloyl group. The importance of the pyrogallol structural motif in the B-ring and the galloyl group was confirmed using methylated catechins and phenolic acids. These results indicate that the most important structural element contributing to the formation of protein carbonyl in HSA by tea catechins is the pyrogallol structural motif in the B-ring, followed by the galloyl group. The oxidation stability and binding affinity of tea catechins with proteins are responsible for the formation of protein carbonyl, and consequently the difference in these properties of each catechin may contribute to the magnitude of their biological activities.

Regioselective synthesis of methylated epigallocatechin gallate via nitrobenzenesulfonyl (Ns) protecting group.

Regioselective synthesis of methylated epigallocatechin gallate from epigallocatechin was accomplished using a 2-nitrobenzenesulfonyl (Ns) group as a protecting group for phenols. This methodology provided several methylated catechins, which are naturally scarce catechin derivatives.

Concise synthesis of chafurosides A and B.

The regioselective synthesis of chafurosides A (1) and B (2) from the same methyl ketone 5 was accomplished using a novel protecting group strategy. Both flavone rings were constructed from beta-diketone intermediate 4, which was readily obtained by condensation of an acyl donor and ketone 5. Construction of the dihydrofuran ring was achieved via an intramolecular Mitsunobu reaction.