Peptides containing the sulfonamide transition‐state isostere: synthesis and structure of N‐acetyl‐tauryl‐l‐proline methylamide

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Abstract
The structure of the sulfonamide isostere‐containing peptide N‐acetyl‐tauryl‐proline methylamide 4 was compared to information on the structure of the peptide N‐acetyl‐β‐alanyl‐proline methylamide 6. NMR measurements of the β‐alanine containing peptide 6 showed the presence of two conformations due to cis/trans isomerism of the β‐Ala‐Pro amide bond, whereas the sulfonamide‐containing peptide 4 appeared in only one conformation. The crystal structure of N‐acetyl‐tauryl‐proline methylamide 4 gave additional evidence for the absence of cis/trans isomerism. The crystals are orthorhombic, space group P212121, Z= 4, F(000) = 592, a= 7.5919(3), b= 10.3822(2), c= 17.1908(7) Å, V= 1354.99(8) Å3, Dx= 1.359 g cm−3. The oxygen atoms connected to the sulfur take positions similar to both the cis and trans positions of the carbonyl oxygen of an amide. Consequently the tauryl part is placed perpendicular to the proline α‐C‐C(O) bond, giving it an extended conformation in contrast to the cis/trans isomers of N‐acetyl‐β‐alanyl‐proline methylamide 6.© Munksgaard 1995.