Kinetic Resolution of 5-Substituted Oxazinones with Bifunctional Chiral Base/Squaramide Organocatalysts

Anion-Binding Properties of Aliphatic Symmetric Squaramide Receptors

Squaramides (SQs), which are very popular for their H-bonding ability, have attracted great interest due to their wide range of applications such as asymmetric synthesis, pharmacology, and anion transportation. In this study, aliphatic symmetric SQs based on cis/trans-1,2-diaminocyclohexane (DACH) substituted with cyclic tertiary amines, synthesized in four steps under simple reaction conditions, were investigated for the first time for their ability to bind Cl-, Br-, and I- anions. The changes in cis/trans geometric isomers and the cyclic ring (pyrrolidine vs piperidine) were found to have a combined effect on the degree of anion binding. The spectroscopic titrations of the SQs with TBA-Cl, TBA-Br, and TBA-I in the range of 0.2 to 20.0 equiv were monitored by 1H NMR, and the analyses of the magnitude of chemical shift differences in the NH peaks of the SQs in course of titration were performed by DynaFit and BindFit programs for the calculation of their Ka values. All symmetric SQs I-IV were found to selectively bind Cl- anion more strongly than Br- anion to varying degrees depending on the SQ derivatives. Especially, SQ IV, which has a symmetric trans-DACH and a pyrrolidine ring, was found to have the highest Cl- anion-binding ability compared to the other SQs. However, the SQs did not show any change in the chemical shift of the NH proton in 1H NMR upon successive addition of TBA-I, indicating that they do not interact with I- anion. The stoichiometries of the complexation behavior of SQs I-IV toward Cl- and Br- anions were also analyzed by Job plots.

Synthesis, structure, and antitumor activity of 2,9-disubstituted perhydro 2,3a,7b,9,10a,14b-hexaazadibenzotetracenes

Catalytic methods for the synthesis of previously unknown 2,9-disubstituted 3bR*,7aR*,10bR*,14aR*-cis-14c,14d-perhydro-2,3a,7b,9,10a,14b-hexaazadibenzotetracenes have been developed. The structures were established by 1D (¹H, ¹³C) and 2D (COSY, HSQC, HMBC) NMR spectroscopy, MALDI TOF/TOF mass spectrometry, and X-ray diffraction analysis. Primary screening of the synthesized perhydro hexaazadibenzotetracenes for antitumor activity was carried out.

Catalytic methods for the synthesis of previously unknown 2,9-disubstituted 3bR*,7aR*,10bR*,14aR*-cis-14c,14d-perhydro-2,3a,7b,9,10a,14b-hexaazadibenzotetracenes with pronounced antitumor activity have been developed.

An organocatalytic domino Michael addition strategy: construction of bispiro[oxindole-thiazolidinone-hexahydroxanthone]s with five contiguous stereocenters

An efficient squaramide-catalyzed domino Michael addition for the stereoselective synthesis of bispiro[oxindole-thiazolidinone-hexahydroxanthone]s in good to excellent yields with excellent stereoselectivities was developed.

Chemical Resolution of C, N-Unprotected α-Substituted β-Amino Acids Using Stable and Recyclable Proline-Derived Chiral Ligands

We report the first purely chemical method for the resolution of C, N-unprotected racemic α-substituted β-amino acids (β²-AAs) using thermodynamically stable and recyclable chiral proline-derived ligands. The ligands and racemic β²-AAs along with Ni(II) could form a pair of Ni(II) complex diastereoisomers with a desirable diastereoselectivity (dr up to 91:9). Enantiomerically pure C, N-unprotected β²-AAs could be obtained by simple hydrolysis of an isolated favored Ni(II) complex. The method featured unique versatility compared with enzymatic approaches and characterized by its broad synthetic generality, good stereochemical outcome, and mild reaction conditions, thus making it a powerful supplement in the field of chemical resolution of β²-AAs.