Enantioselective alkylation ofα-amino carbanions

Consecutive Lossen rearrangement/transamidation reaction of hydroxamic acids under catalyst- and additive-free conditions

The Lossen rearrangement is a classic process for transforming activated hydroxamic acids into isocyanate under basic or thermal conditions. In the current report we disclosed a consecutive Lossen rearrangement/transamidation reaction in which unactivated hydroxamic acids were converted into N-substituted formamides in a one-pot manner under catalyst- and additive-free conditions. One feature of this novel transformation is that the formamide plays triple roles in the reaction by acting as a readily available solvent, a promoter for additive-free Lossen rearrangement, and a source of the formyl group in the final products. Acyl groups other than formyl could also be introduced into the product when changing the solvent to other low molecular weight aliphatic amide derivatives. The solvent-promoted Lossen rearrangement was better understood by DFT calculations, and the intermediacy of isocyanate and amine was supported well by experiments, in which the desired products were obtained in excellent yields under similar conditions. Not only monosubstituted formamides were synthesized from hydroxamic acids, but also N,N-disubstituted formamides were obtained when secondary amines were used as precursors.

Synthesis of substituted tetrahydroisoquinolines by lithiation then electrophilic quench

Lithiation then electrophilic quench of tetrahydroisoquinolines provides access to 1-substituted products. Removal of the N-Boc group allows rapid access to natural products such as (±)-crispine A.

Synthesis of Novel Chiral (Thio)ureas and Their Application as Organocatalysts and Ligands in Asymmetric Synthesis

The synthesis of novel chiral (thio)ureas 1–10 and 14–26 is described. These (thio)ureas incorporate chiral auxiliaries derived from (R)- or (S)-α-phenylethylamine, (R)-phenylglycine, or (1R,2S)-ephedrine. The phenylethyl group in compounds 1–10 and 21–24 adopts a particular orientation in the molecular structure as a consequence of 1,3-allylic strain with the (thio)carbonyl group. Ureas 1–10 were tested as Lewis basic organocatalysts in epoxide ring opening and in aldolic condensation, and it was found that the tetrasubstituted urea (R,R)-2 afforded the best results in terms of reaction yields. (Thio)ureas 20–26 were examined as ligands in the enantioselective diethylzinc addition to benzaldehyde, observing that C2-symmetric chiral urea (R,S,R,S)-20 provides the expected carbinol in nearly quantitative yield and in up to 62% enantiomeric excess.

Synthesis and neurotoxicity of tetrahydroisoquinoline derivatives for studying Parkinson's disease

Parkinson's disease involves the progressive degeneration of dopaminergic neurons in the substantia nigra. However, the etiology of the disease remains to be elucidated. Endogenous amines, such as 1,2,3,4-tetrahydroisoquinoline (TIQ) derivatives present in the mammalian brain, are known to participate in the pathogenesis of Parkinson's disease. These endogenous neurotoxins have been extensively studied because of their structural resemblance to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), an agent widely used for generating animal models of Parkinson's disease-like symptoms. Investigations of the synthesis and pharmacological properties of TIQ derivatives are expected to contribute to the development of new therapeutic agents for treating Parkinson's disease. In the present study, we describe more efficient synthesis methods for TIQ derivatives via Pummerer-type cyclization of the substrate N-acyl sulfoxide. Furthermore, the modified Pummerer reaction provided a convenient and efficient method for synthesizing various TIQs. TIQ and its derivative, 1-benzyl-TIQ, can induce parkinsonism in primates and rodents. On the other hand, one TIQ derivative, 1-methyl-TIQ, has been shown to prevent MPTP, TIQ, and 1-benzyl-TIQ induced behavioral abnormalities. Therefore, TIQ derivatives are considered to play an important role in both the onset and prevention of Parkinson's disease. In this article, we focus on the synthesis and pharmacological aspects of 1,2,3,4-tetrahydroisoquinoline derivatives in Parkinson's disease.