Molecular and crystal structures of two N α -protected α-aminoacyl fluorides and their free carboxylic acid synthetic precursors 1

Methyl-2-methyl-2-(4-methyl-phenyl)sulfonamido propanoate: structural study, supramolecular architecture and analysis of molecular surface electrostatic potential

An arylsulfonamide compound, methyl-2-methyl-2-(4-methylphenyl)sulfonamido propanoate, (1), has been synthesised and structurally characterised. Compound (1) has a staggered conformation relative to the S–N bond. The DFT-optimised molecular geometry of (1) agrees closely with that obtained from the crystallographic study. The crystal exhibits cooperation of N–H···O hydrogen bonds with C–H···O and C–H···π(arene) interactions, resulting in a three-dimensional framework featuring R2 2(8) and R2 2(10) synthons. The effect of substitution in different arylsulfonamides retrieved from the Cambridge Structural Database (CSD) on the formation of supramolecular synthons has been analysed in terms of graph-set notation. Hydrogen-bond based interactions in (1) have been complemented by molecular electrostatic potential (MEP) surface calculation. Hirshfeld surface analyses of (1) and a few related arylsulfonamides retrieved from the CSD indicate that about 80% of the Hirshfeld surface areas in these compounds are due to H···H and O···H contacts.

Reactive intermediates in peptide synthesis. Molecular and crystal structures of reactive carboxylic amides

The molecular and crystal structures of N-para-toluenesulphonyl-N-methyl-α-aminoisobutyric acyl imidazole (1), and 3-(N-para-toluenesulphonyl-α-aminoisobutyric acyl)-1,3-thiazolidine-2-thione (2) have been determined by X-ray diffraction. Crystal parameters: (1) orthorhombic, space group P212121, a = 11.735(2) Å, b = 19.990(3) Å, c = 6.925(1) Å, and Z = 4; (2) orthorhombic, space group Pnc2, a = 9.507(2) Å, b = 16.902(2) Å, c = 10.347(2) Å, and Z = 4. The structures were solved by direct methods. The least-squares refinements led to conventional R factors of 0.036 and 0.031 for (1) and (2), respectively. This is the first geometrical and conformational characterization at atomic resolution of N α -protected α-aminoacids containing the elusive acyl imidazole and 3-acyl-1,3-thiazolidine-2-thione C-activating groups. Only the reactive carboxylic amide of (2) deviates significantly from planarity.