1. α-Imino Esters in Organic Synthesis: Recent Advances
Bagher Eftekhari-Sis, Maryam Zirak Chem Rev . 2017 Jun 28;117(12):8326-8419. doi: 10.1021/acs.chemrev.7b00064.
α-Imino esters are useful precursors for the synthesis of a variety of types of natural and unnatural α-amino acid derivatives, with a wide range of biological activities. Due to the adjacent ester group, α-imino esters are more reactive relative to other types of imines and undergo different kinds of reactions, including organometallics addition, metal catalyzed vinylation and alkynylation, aza-Henry, aza-Morita-Baylis-Hillman, imino-ene, Mannich-type, and cycloaddition reactions, as well as hydrogenation and reduction. This review discusses the mechanism, scope, and applications of the reactions of α-imino esters and related compounds in organic synthesis, covering the literature from the last 12 years.
2. [Evaluation of the Oral Absorption of Ester-type Prodrugs]
Kayoko Ohura Yakugaku Zasshi . 2020;140(3):369-376. doi: 10.1248/yakushi.19-00225.
The first-pass hydrolysis of oral ester-type prodrugs in the liver and intestine is mediated mainly by hCE1 and hCE2 of the respective predominant carboxylesterase (CES) isozymes. In order to provide high blood concentrations of the parent drugs, it is preferable that prodrugs are absorbed as an intact ester in the intestine, then rapidly converted to active parent drugs by hCE1 in the liver. In the present study, we designed a prodrug of fexofenadine (FXD) as a model parent drug that is resistant to hCE2 but hydrolyzed by hCE1, utilizing the differences in catalytic characteristics of hCE1 and hCE2. In order to precisely predict the intestinal absorption of an FXD prodrug candidate, we developed a novel high-throughput system by modifying Caco-2 cells. Further, we evaluated species differences and aging effects in the intestinal and hepatic hydrolysis of prodrugs to improve the estimation of in vivo first-pass hydrolysis of ester-type prodrugs. Consequently, it was possible to design a hepatotropic prodrug utilizing the differences in tissue distribution and substrate specificity of CESs. In addition, we successfully established three useful in vitro systems for predicting the intestinal absorption of hCE1 substrate using Caco-2 cells. However, some factors involved in estimating the bioavailability of prodrugs in human, such as changes in recognition of drug transporters by esterification, and species differences of the first-pass hydrolysis, should be comprehensively considered in prodrug development.
3. Palladium-Catalyzed Tandem Ester Dance/Decarbonylative Coupling Reactions
Eisuke Ota, Naomi Inayama, Junichiro Yamaguchi, Masayuki Kubo Org Lett . 2022 Jun 3;24(21):3855-3860. doi: 10.1021/acs.orglett.2c01432.
"Dance reaction" on the aromatic ring is a powerful method in organic chemistry to translocate functional groups on arene scaffolds. Notably, dance reactions of halides and pseudohalides offer a unique platform for the divergent synthesis of substituted (hetero)aromatic compounds when combined with transition-metal-catalyzed coupling reactions. Herein, we report a tandem reaction of ester dance and decarbonylative coupling enabled by palladium catalysis. In this reaction, 1,2-translocation of the ester moiety on the aromatic ring is followed by decarbonylative coupling with nucleophiles to enable the installation of a variety of nucleophiles at the position adjacent to the ester in the starting material.