Asymmetric synthesis of two new conformationally constrained lysine derivatives

The Bucherer-Bergs Multicomponent Synthesis of Hydantoins-Excellence in Simplicity

Hydantoins and their hybrids with other molecules represent a very important group of heterocycles because they exhibit diverse biological and pharmacological activities in medicinal and agrochemical applications. They also serve as key precursors in the chemical or enzymatic synthesis of significant nonnatural α-amino acids and their conjugates with medical potential. This review provides a comprehensive treatment of the synthesis of hydantoins via the Bucherer-Bergs reaction including the Hoyer modification but limited to free carbonyl compounds or carbonyl compounds protected as acetals (ketals) and cyanohydrins used as starting reaction components. In this respect, the Bucherer-Bergs reaction provides an efficient and simple method in the synthesis of important natural products as well as for the preparation of new organic compounds applicable as potential therapeutics. The scope and limitations, as well as a comparison with some other methods for preparing hydantoins, are also discussed.

On the Origin of the Promoting Effect Exerted by Magnesium in the ZnCl2-Catalyzed Synthesis of N,N-Diisopropylethylamine

The reaction of magnesium or zinc amides with alkyl or benzyl halides is an attractive approach to make C-N bonds, especially for electron-poor organic halides. The magnesium-promoted preparation of hindered non-nucleophilic amine (N,N-diisopropylethylamine) from ethyl chloride and zinc diisopropylamide has been studied. In this paper, instead of the application scope of this method, we focused on the mechanisms of the catalytic processes and the associated electronic origins. According to the calculations, the C-N coupling process in all selected systems proceed preferably in an ethylium-transfer mode. Further, rather than undergoing the Grignard reaction route, the more pronounced electronic interactions within the transition structure as induced by the "innocent" magnesium atom should be responsible for the observed high catalytic activity of the Mg/ZnCl₂ combination.

Structure-activity relationship of N-benzenesulfonyl matrinic acid derivatives as a novel class of coxsackievirus B3 inhibitors

A novel series of N-benzenesulfonyl matrinic amine/amide and matrinic methyl ether analogues were designed, synthesized and evaluated for their in vitro anti-coxsackievirus B3 (CVB3) activities. The structure-activity relationship (SAR) studies revealed that introduction of a suitable amide substituent on position 4' could greatly enhance the antivirus potency. Compared to the lead compounds, the newly synthesized matrinic amide derivatives 21c-d and 21j exhibited stronger anti-CVB3 activities with lower micromolar IC50 from 2.5 μM to 2.7 μM, and better therapeutic properties with improved selectivity index (SI) from 63 to 67. The SAR results provided powerful information for further strategic optimization, and these top compounds were selected for the next evaluation as novel enterovirus inhibitors.

RANEY® nickel-catalyzed reductive N-methylation of amines with paraformaldehyde: theoretical and experimental study

RANEY® Ni-catalyzed reductive N-methylation of amines with paraformaldehyde has been investigated.

Conformationally constrained histidines in the design of peptidomimetics: strategies for the χ-space control

A successful design of peptidomimetics must come to terms with χ-space control. The incorporation of χ-space constrained amino acids into bioactive peptides renders the χ¹ and χ² torsional angles of pharmacophore amino acids critical for activity and selectivity as with other relevant structural features of the template. This review describes histidine analogues characterized by replacement of native α and/or β-hydrogen atoms with alkyl substituents as well as analogues with α, β-didehydro unsaturation or C^α-C^β cyclopropane insertion (ACC derivatives). Attention is also dedicated to the relevant field of β-aminoacid chemistry by describing the synthesis of β²- and β³-models (β-hHis). Structural modifications leading to cyclic imino derivatives such as spinacine, aza-histidine and analogues with shortening or elongation of the native side chain (nor-histidine and homo-histidine, respectively) are also described. Examples of the use of the described analogues to replace native histidine in bioactive peptides are also given.

Conformationally-restricted amino acid analogues bearing a distal sulfonic acid show selective inhibition of system x(c)(-) over the vesicular glutamate transporter

A panel of amino acid analogs and conformationally-restricted amino acids bearing a sulfonic acid were synthesized and tested for their ability to preferentially inhibit the obligate cysteine-glutamate transporter system x(c)(-) versus the vesicular glutamate transporter (VGLUT). Several promising candidate molecules were identified: R/S-4-[4'-carboxyphenyl]-phenylglycine, a biphenyl substituted analog of 4-carboxyphenylglycine and 2-thiopheneglycine-5-sulfonic acid both of which reduced glutamate uptake at system x(c)(-) by 70-75% while having modest to no effect on glutamate uptake at VGLUT.

Recent Progress on the Stereoselective Synthesis of Cyclic Quaternary alpha-Amino Acids

The most recent papers describing the stereoselective synthesis of cyclic quaternary alpha-amino acids are collected in this review. The diverse synthetic approaches are classified according to the size of the ring and taking into account the bond that is formed to complete the quaternary skeleton.