Structural diversity using amino acid "Customizable Units": conversion of hydroxyproline (Hyp) into nitrogen heterocycles

The ability of amino acid “customizable units” to generate structural diversity is illustrated by the conversion of 4-hydroxyproline (Hyp) units into a variety of nitrogen heterocycles. After a first common step, where the unit underwent a one-pot decarboxylation–alkylation reaction to afford 2-alkylpyrrolidines with high stereoselectivity, a divergent step was carried out. Thus, the deprotected 4-hydroxy group was used either to initiate a radical scission that afforded aliphatic β-amino aldehydes, or to carry out an elimination reaction, to give 2-alkyl-2,5-dihydro-1H-pyrroles. In the first case, the amines underwent a tandem reductive amination–cyclization to afford β-amino-δ-lactams, an efficient rigidifying unit in peptides. Different lactam N-substituents, such as alkylamines, peptides, and alkenyl chains suitable for olefin metathesis were introduced this way. In the second case, the pyrrole derivatives were efficiently converted into alkaloid and iminosugar derivatives in good global yields and with excellent stereoselectivity.

New approaches towards the synthesis of 1,2,3,4-tetrahydro isoquinoline-3-phosphonic acid (TicP)

Two new strategies for the efficient synthesis of racemic 1,2,3,4-tetrahydroisoquinoline-3-phosphonic acid (Tic^P) (±)-2 have been developed. The first strategy involves the electron-transfer reduction of the easily obtained α,β-dehydro phosphonophenylalanine followed by a Pictet-Spengler cyclization. The second strategy involves a radical decarboxylation-phosphorylation reaction on 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic). In both strategies, the highly electrophilic N-acyliminium ion is formed as a key intermediate, and the target compound is obtained in good yield using mild reaction conditions and readily available starting materials, complementing existing methodologies and contributing to the easy accessibility of (±)-2 for further research.