Accutof jms t100lc

High-resolution mass spectra were recorded using a JEOL AccuTOF JMS T100LC instrument fitted with an electrospray ion source. The spectrum was recorded over the mass range 50–1000 m/z.
UV-Vis absorption spectra were recorded on-line during HPLC analysis over the wavelength range 240–600 nm in steps of 2 nm.
NMR samples were prepared by dissolving the isolated compounds in hexadeuterated dimethylsulfoxide (99.9 atom % D, Sigma-Aldrich). The 1D ¹H and the 2D ¹H-¹³C HMBC, ¹H-¹³C HSQC, 2D ¹H-¹H COSY and ¹H-¹H ROESY NMR experiments were obtained at 600.13 MHz and 150.90 MHz for ¹H and ¹³C, respectively, at 298K on a Bruker 600 MHz instrument equipped with a cryogenic probe.

NMR spectra, including
bidimensional, were recorded in CD₃OD, CDCl₃, or DMSO-δ₆ solution on a Bruker Avance III HD
or Bruker BioSpin (Billerica, MA) spectrometer at either 700 or 400
MHz (¹H) and 175 or 100 MHz (¹³C), using TMS
as an internal standard. High-resolution mass spectra, HRMS (ESI-TOF⁺), were acquired with a JEOL AccuTOF JMS-T100LC (Peabody,
MA) spectrometer. Optical rotation was obtained with an Anton Paar
MCP 150 polarimeter. Gas chromatography–mass spectrometry (GC–MS)
determinations were made using an Agilent 5975C system equipped with
a 30 m DB-5MS capillary column (0.25 mm i.d.; 0.25 mm). Preparative
HPLC was carried out with a Waters instrument (Milford, MA) equipped
with a 2535 pump and a 2998 photodiode array detector, using an XBridge
Prep Shield RP-C18 (19.0 × 250 mm², 5 mm particle
size) packed column, and different gradient systems of MeCN and 0.1%
aqueous formic acid, at a flow rate of 17.06 mL/min. Control of equipment,
data acquisition and processing, and management of chromatographic
information were performed using the Empower 3 software package. Column
chromatography (CC) was carried out on silica gel 60 (Merck, Darmstadt,
Germany) or Sephadex LH-20 (GE Healthcare, Little Chalfont, Buckinghamshire,
U.K.). Thin-layer chromatographic (TLC) analyses were performed on
silica gel 60 F254 plates (Merck) and visualized using a Ce₂(SO₄)₃ (10%) solution in H₂SO₄.

All reagents and organic solvents were used as received from commercial resources without further purification. 1,3-dihydro-1-hydroxy-2,1-benzoxaborole-5-carboxylic acid (2-COOH) was synthesised according to the literature method (Scheme S1†).^{16 (link)} Milli-Q water was used for spectroscopic measurements.
¹H and ¹³C nuclear magnetic resonance (NMR) spectra were acquired with a JEOL JNM-ECA 500 spectrometer (JEOL, Japan) at room temperature. High resolution electrospray ionization mass spectra (ESI-HRMS) were measured using a JEOL The Accu-TOF JMS T100LC (JEOL, Japan). The pH of solutions was measured by a HORIBA pH electrode 9618S-10D connected to a HORIBA pH meter F-52 (Horiba, Japan). UV-vis absorption spectra were obtained at 25 °C using a Hitachi U-3900H spectrophotometer (Hitachi, Japan) equipped with a temperature controller (Hitachi, Japan). Fluorescence spectra were recorded at 25 °C using a Hitachi F-7000 fluorescence spectrophotometer (Hitachi, Japan) equipped with a temperature controller (Hitachi, Japan) and an EYELA CCA-1111 (EYELA, Japan). Induced circular dichroism spectra were recorded at 25 °C using a JASCO J-820 spectrophotometer (JASCO, Japan) equipped with a Peltier temperature controller (JASCO, Japan) and an EYELA Cool Ace CA-1111 (EYELA, Japan) under a nitrogen atmosphere.