11B and 1H-11B HMBC NMR as a Tool for Identification of a Boron-Containing Nucleoside Dimer

Abstract

Boron-containing compounds are commonly used in synthetic chemistry and are known to play important roles in biology. Despite the widespread relevance of boronated compounds, there have been limited methods to discover, characterize, and study them. Here, we describe the use of ¹¹B NMR, including ¹H-¹¹B HMBC, for the isolation and characterization of the boron-containing natural product diadenosine borate. Utilizing synthetic standards, we optimized coupling parameters for ¹H-¹¹B HMBC experiments to allow for the analysis of small quantities (∼1 mg) of boron-containing compounds. This work can facilitate the broader application of ¹¹B NMR to the study of boron in a range of applications, from synthetic chemistry to the role of boron in naturally occurring systems.

Figure 1

Boron-containing natural products.

Figure 2

¹¹B NMR of semicrude SNE-036 extract (200 mg, 256 scans, top) and pure compound 4 (1 mg, 512 scans, bottom) in D₂O with potential boron species.^,

Figure 3

(a) Structure of compound 4. (b) ¹H NMR of 1 mg of synthetic (top) and isolated (bottom) 4 in D₂O.

Figure 4

Previously reported synthetic boron-containing nucleoside analogs.⁻

Figure 5

(a) Concentration vs absolute integration of 2 h 1D ¹H–¹¹B HMBC for 2-methylphenyl boronic acid (2-MPBA) in CD₃OD. (b) One-dimensional ¹H–¹¹B HMBC plots for different concentrations of 2-MPBA.

Figure 6

(a) Experiment time (h) vs absolute integration of 1D ¹H–¹¹B HMBC and 2D ¹H–¹¹B HMBC for 2-MPBA in CD₃OD. (b) Four hour 1D ¹H–¹¹B HMBC of 10 mM 2-MPBA. (c) Four hour 2D ¹H–¹¹B HMBC of 10 mM 2-MPBA.

Figure 7

Two-dimensional ¹H–¹¹B HMBC of 4 (1 mg, 720 scans) in D₂O.