Structural assignment of regioisomeric 3-[2- or 5-anilino-2-(alkylamino)phenyl]propanoic acids, 2H-1,4-benzothiazin-3(4H)-ones and 2,3-dihydro-1,5-benzothiazepin-4(5H)-ones by 1D NOE and gHMBC NMR techniques

The 1H and 13C NMR spectra of compounds 1-11 and 16-22 in CDCl3 and DMSO-d6 solutions allowed structural assignment to regioisomers 1/5 and 2/6 and their regioselective cyclization products 16-18 utilizing one- and two-dimensional NMR techniques (APT, DEPT, NOE difference, COSY, NOESY, HETCOR and gHMQC, gHMBC). Temperature-dependent 1H NMR spectra of 8-anilino-5-(4-methyl-2-pentyl)-2,3-dihydro-1,5-benzothiazepin-4(5H)-one (18) indicated a free energy of activation (deltaG++) of ca 17 kcal mol(-1) for interconversion between rotamers. The 1H and 13C NMR spectra of 20 and 22 containing two chiral centers exhibit duplication of several signals, indicating the existence of two diastereomeric forms. The structure of 4 was unambiguously confirmed by x-ray crystallography.