Structure and conformation of peptides containing the sulphonamide junction. III. Synthesis, crystal and molecular structure of a taurine containing peptidic oxa-cyclol.
The insertion of the (S)-lactyl residue into the cyclodipeptide cyclo (-Tau-Pro-) 3 leads in good yields to the first example of a stable tetrahedral adduct (oxa-cyclol) 5 containing the sulphonamide junction. Compound 5 does not show a significant tendency towards tautomeric equilibria and possesses an unexpected syn-orientation involving the hydroxyl group and the Pro-H alpha. The crystal structure and molecular conformation of 5 has been determined. Crystals are orthorhombic, s.g. P2(1)2(1)2(1), with a = 6.607, b = 12.297, c = 16.622 A. The cisoidal conformation around the S-N bond is very similar to that found in the previously studied linear and cyclic peptides containing a sulphonamide junction. The taurine nitrogen is practically planar whereas the proline nitrogen, bound to the SO2 group, is highly pyramidal. In the tricyclic system of 5 the seven-membered ring adopts a twist-chair conformation while the pyrrolidine and oxazolidinone rings show an envelope conformation. The crystal packing is characterized by three hydrogen bonds all formed by means of a water molecule.
Calcagni
A
A
Department of Pharmaceutical Studies, University La Sapienza, Rome, Italy.
Gavuzzo
E
E
Lucente
G
G
Mazza
F
F
Pinnen
F
F
Pochetti
G
G
Rossi
D
D
D000595:Amino Acid Sequence; D003461:Crystallography; D008969:Molecular Sequence Data; D010456:Peptides, Cyclic / Q000138:chemical synthesis / Q000737:chemistry*; D011487:Protein Conformation; D013329:Structure-Activity Relationship; D013449:Sulfonamides / Q000138:chemical synthesis / Q000737:chemistry*
D010456:Peptides, Cyclic; D013449:Sulfonamides; C070148:oxa-glycol