Complete assignment of the ¹H and ¹³C NMR spectra of antimicrobial 4‐arylamino‐ 3‐nitrocoumarin derivatives

Abstract

Herein, we describe the synthesis and complete assignment of the (1)H and (13)C NMR chemical shifts of a series of antimicrobial 4-arylamino-3-nitrocoumarin derivatives based on a combination of (1)H and (13)C NMR, (1)H-(1)H-COSY, NOESY, HSQC and HMBC experiments. Conformational effects upon the chemical shifts of the coumarin moiety arising from the anisotropy of the aryl side group are briefly discussed. This study provides the first complete and fully assigned NMR data for this important group of antimicrobial compounds and bridges the gap existing in the literature with regard to NMR structural data for 4-arylamino-3-nitrocoumarins.

Influence of the aryl substituent identity in 4-arylamino-3-nitrocoumarins on their antimicrobial activity

“…HRMS(EI): M + (C16H12N2O4) 296.0815, requires 296.0797 (= +1.8 mmu). IR and 1 H and 13 C NMR (in CDCl3) previously published (Tabaković et al, 1983;Dekić et al, 2010c 2H, H-6, H-8), 7.00-7.20 (m, 4H, H-2', H-3', H-5', H-6'), 2.31 (s, 3H, CH3).…”

“…HRMS(EI): M + (C15H11N3O4) 297.0743, requires 297.0750 (= -0.7 mmu). IR and 1 H and 13 C NMR (in CDCl3) previously published (Dekić et al, 2010c). IR (neat, cm −1 ): 3371-3068 (N-H and Ar-H), 1710 (C=O), 1605 (C=C), 1549 and 1332 (NO2), 1240, 1056, 945, 782, 756. 1 H NMR (DMSO-d6, ppm):  = 10.07 (brs, 1H, N-H), 8.38 (dd, 1H, H-5, J = 8.5, 1.5 Hz), 7.74 (dt, 1H, H-7, J = 8.5, 1.5 Hz), 7.41-7.48 (m, 2H, H-6, H-8), 6.82-6.92 (dd, 2H, H-2', H-6' J = 8.6, 2.0 Hz), 6.45-6.54 (dd, 2H, H-3', H-5' J = 8.6, 2.0 Hz), 5.32 (s, 2H, NH2).…”

“…IR and 1 H NMR (in CDCl3) previously published (Savel'ev et. al., 1989;Dekić et al, 2010c). IR (neat, cm …”

“…HRMS(EI): M + (C16H12N2O4) 296.0781, requires 296.0797 (= -1.6 mmu). IR and 1 H and 13 C NMR (in CDCl3) previously published (Dekić et al, 2010c 13 C NMR (DMSO-d6, ppm):  = 155.1, 151.6, 145.6, 137.9, 137.8 (two C), 137.6, 134.6, 125.4 (two C), 124.8, 117.8, 117.6, 114.6, 91.7.…”

“…With all of this in mind and in the continuation of our previous work, it seemed that there is further room for improvement of the observed activity of these coumarin derivatives. We decided to synthesize several new and structurally similar, already reported on (Dekić et al, 2010c), 4-arylamino-3-nitrocoumarins and test their in vitro antibacterial and antifungal activities, and compare the obtained results with the antimicrobial activity of previously synthesized 4-heteroarylamino-3-nitrocoumarins (Dekić et al, 2010a, b), in hope of reaching a somewhat broader perspective of the scope of this activity.…”