Intramolecular hydrogen bonds in sulfur-containing aminophenols

Abstract

a sulfonamide fragment but also conformational equilibrium among these types of intramolecular interactions are essential for the manifestation of high efficiency in suppressing HIV-infection in cell culture.Introduction. Many derivatives of aminophenols (AP) are known to be effective antioxidants that are capable of changing the course of free-radical processes [1]. These compounds also have traditional applications as stabilizers of industrial organic materials and as food preservatives [2,3]. They exhibit high efficiency for prevention and treatment of pathologies due to disorders in the human antioxidant system [4] and as antiviral agents against herpes simplex and flu A virus [5][6][7][8][9]. AP derivatives that suppress HIV-infection in cell culture were recently synthesized [10].The pharmacological properties of AP are related to their effect on the course of free-radical processes in biological systems. Steady-state radiolysis and IR spectroscopic methods found that the antioxidant properties of AP are enhanced when the hydroxyls in the molecules are free and diminished upon forming various types of intramolecular hydrogen-bonds (IHB) [11]. As a rule, reactions involving active oxygen species occur nonselectively. Their occurrence in biological systems can damage both the cells themselves and viruses incorporated into them if highly active antioxidants are used.The question of which AP derivatives that are added to biological systems can change the course of free-radical reactions so that an effective and stable antiviral effect is obtained remains open. Therefore, it is important in principle to study properties of individual molecules such as the ability to form IHB because the type of IHB found in the AP is frequently related to their antiradical and antiviral activity [12,13].Herein IR-Fourier spectroscopy is used to study intramolecular interactions (IMI) in CCl 4 solutions of five structurally similar AP derivatives, 4,6-di-tert-butyl-2-(phenylamino)phenol (AP I), N-(3,5-di-tert-butyl-2-hydroxyphenyl)acetamide (AP II), N-(2-hydroxy-3,5-di-tert-butylphenyl)-4-methylbenzenesulfonamide (AP III), N-(2-methoxy-3,5-di-tert-butylphenyl)-4-methylbenzenesulfonamide (AP IV), and N-(2-hydroxy-3,5-di-tert-butylphenyl) methanesulfo-namide (AP V):

Intramolecular and intermolecular hydrogen bonds in aminophenols

“…Solutions of AP in CCl 4 (10 -3 M) and AP powders pressed in KBr were studied in order to establish the nature of IaMI and IrMI in the AP derivatives. For AP concentrations of 10 -3 M in neutral solvents, IrMI were practically non-existent [17][18][19][20][21][22]. Powders were triturated with anhydrous finely dispersed KBr and pressed in vacuo.…”

“…Figure 1 shows IR spectra in the range 3700-2700 cm -1 for AP I-AP VI in CCl 4 solutions and pressed in KBr. This spectral region contains AB for stretching vibrations of OH and NH groups that are most capable in AP of IaMI and IrMI [18] and AB for C-H vibrations in the aromatic ring and methyl, methylene, and tert-butyl groups. Bands for C-H stretching vibrations were characteristic of all compounds and practically did not shift upon going from solution to the solid state [18].…”

Intramolecular interactions of N-(3,5-di-tert-butyl-2-hydroxyphenyl)acetamide derivatives

“…The nature of the IMI was established using IR-Fourier spectroscopy of solutions of AP (10 -3 M) in CCl 4 . Intermolecular interactions of AP at these concentrations in neutral solvents are practically non-detectable [9][10][11][12]. IR spectra of AP solutions were recorded on a Nexus IR-Fourier spectrometer with OMNIC software in the range 4000-1500 cm -1 with spectral resolution 2 cm -1 and averaging over 256 scans.…”

“…The hydroxyl on the benzene ring in all examined AP was located in the o-position to the amino group. Various types of IHB involving these groups can form for AP solutions in neutral solvents with the OH and NH groups in such positions [9][10][11][12]. The studied compounds also typically had a C=O group that was bonded to the N atom and could participate in IMI [12].…”

“…IR spectra of CCl 4 solutions of AP were studied in the range 3700-2600 cm -1 , where absorption bands (AB) for stretching vibrations of free and associated OH-and NH-groups are located, in order to find the role of OH, NH, and C=O groups in IMI [9][10][11][12]. Figures 1a, 2a, and 3a show this spectral range and the corresponding AB.…”