¹⁵N¹H and ¹⁵N–¹³C couplings in ¹⁵N‐enriched dihydroxamic acids

Abstract

(15)N-enriched dihydroxamic acids (HONHCO(CH(2))(n)CONHOH, n = 0, 1, and 2) were prepared and their spectra NMR ((1)H, (13)C, (15)N) recorded in dimethyl sulfoxide (DMSO) solutions with the aim of determining (15)N coupling constants ((15)N-(1)H and (15)N-(13)C). The results supplement chemical shifts published earlier and yield additional support to the structural conclusions derived from other NMR parameters. Notably, no trace of hydroximic structures could be found in the (15)N NMR spectra of these acids. The values of (15)N-(13)C coupling constants backed by theoretical calculations support the assignments made earlier for all of the major conformers and for the minor conformer of succinohydroxamic acid. The enrichment revealed that the minor component of malonodihydroxamic acid solution previously considered to be the ZE conformer is in fact the monohydroxamic acid (HOOC-CH(2)-CO-NH-OH).

p-Hydroxyacetophenone Amides from Cystobacter ferrugineus, strain Cb G35

“…Similar adequate reference 13 C signals of the other carbon types were not available for calculations. In addition, the 1 H NMR spectrum showed broad doublets for the aromatic protons of the 13 C-labeled part of the sample with a direct 13 C, 1 H coupling 1 J C,H ≈ 150 Hz . Compared to the unlabeled aromatic 1 H signals H-2,6 and H-3,5 (integral 3.74 and 2.88), the doublets for H-2,6 and H-3,5 (integral 3.81 and 3.22) indicated 52% 13 C incorporation, fully supporting the 13 C NMR result (spectrum 37, Supporting Information).…”

“…In addition, the 1 H NMR spectrum showed broad doublets for the aromatic protons of the 13 C-labeled part of the sample with a direct 13 C, 1 H coupling 1 J C,H ≈ 150 Hz. 14 Compared to the unlabeled aromatic 1 H signals H-2,6 and H-3,5 (integral 3.74 and 2.88), the doublets for H-2,6 and H-3,5 (integral 3.81 and 3.22) indicated 52% 13 C incorporation, fully supporting the 13 C NMR result (spectrum 37, Supporting Information). In order to assess the incorporation of 15 N, the broad 1 H doublet signal of the 15 N-labeled NH proton (integral 0.42) with a direct coupling of 1 J N,H ≈ 95 Hz was compared to the broad unlabeled singlet NH signal (integral 1.0) in the 1 H NMR spectrum to give a 15 N incorporation of 30% (spectrum 37, Supporting Information).…”

Hydroxamic Acids As a Novel Family of Serine Racemase Inhibitors: Mechanistic Analysis Reveals Different Modes of Interaction with the Pyridoxal-5′-phosphate Cofactor

“…The instrumental setup and experimental parameters have been described. 41 Mass spectral data were recorded using a Q-TOF microspectrometer from Waters Co. (Milford, MA, USA). UV/vis absorbance scans were conducted on a Unicam UV500 UV/vis spectrophotometer.…”

Computational1H and13C NMR in structural and stereochemical studies

“…In the paper by Schraml and Cigler, [ 250 ] theoretical calculations of 13 C‐ 1 H coupling constants were performed for three dihydroxamic acids, namely, oxalodihydroxamic acid ( 27 ), malonodihydroxamic acid ( 28 ), and succinodihydroxamic acid ( 29 ). Those calculations supported the assignments of all of their major conformers, ZZ , ZE , and EE , exemplified below for 27 .…”