Merck silica gel 60 f254 plates

Unless otherwise noted all the starting materials and reagents were used without further purification. Thin layer chromatography was carried out using Merck silica gel 60 F₂₅₄ plates (Merck, Kenilworth, NJ, USA), and flash chromatography was performed manually using Merck silica gel 60 (0.040–0.063 mm, 230–400 mesh, Merck, Kenilworth, NJ, USA). ¹H- and ¹³C-NMR spectra were recorded using JEOL-500 (JEOL, Tokyo, Japan). ¹H- and ¹³C-NMR chemical shifts are recorded in parts per million (ppm), with the residual solvent peak used as an internal reference. ¹H-NMR data were reported in the order of chemical shift, multiplicity (brs, broad singlet; s, singlet; d, doublet; t, triplet; q, quartet; quint., quintet; m, multiplet and/or multiple resonances), number of protons, and coupling constant in Hertz (Hz). High-resolution mass spectra were obtained with Q Exactive Mass Spectrometer (Thermo Scientific, Waltham, MA, USA).

All solvents were purified using appropriate drying agents and stored over 3 Å molecular sieves. Thin layer chromatography (TLC) was carried out using Merck silica gel 60F-254 plates (Merck, Darmstadt, Germany), while Fluka 0.063–0.2 mm silica gel (Fluka, Neu-Ulm, Germany) was applied for purification by column chromatography. Melting points (m.p.) were determined on Kofler micro hot-stage (Reichert, Wien, Austria). ¹H and ¹³C APT (Attached Proton Test) NMR (nuclear magnetic resonance) spectra were recorded in DMSO-d₆ on a Varian Gemini 300 (at 300 and 75 MHz) or Varian Gemini 600 (at 600 and 150 MHz) (Figures S4–S23). Chemical shifts (б) were referenced to the residual solvent signal of DMSO at б 2.50 ppm for ¹H and б 39.50 ppm for ¹³C. Individual resonances were assigned on the basis of their chemical shifts, signal intensities, multiplicity of resonances and H-H coupling constants. High performance liquid chromatography was performed on an Agilent 1100 series system with UV detection (photodiode array detector). Zorbax C18 reverse-phase analytical column (2.1 × 30 mm, 3.5 µm) was used. All novel compounds showed 95% purity in this HPLC (high performance liquid chromatography) system. Microwave-assisted syntheses were performed in a Milestone start S microwave oven using quartz cuvettes.

The structures of sugar-based aromatic esters (Figure 6) were unambiguously assessed by MS, ¹H NMR, and ¹³C NMR. The ESI-MS spectra were recorded with a Waters Micromass^® ZQ™ (Waters Corporation, Milford, MA, USA) spectrometer in negative or positive mode using a nebulizing nitrogen gas at 400 L/min and a temperature of 250 °C, cone flow of 40 mL/min, capillary of 3.5 kV, and cone voltage of 60 V; only the molecular ions [M − H]⁻, [M + NH₄]⁺, [M + Na]⁺, and [M + HCOO]⁻ were given. ¹H NMR and ¹³C NMR spectra were recorded on a Bruker AC 400 or 101 (Bruker, Billerica, MA, USA) spectrometer, respectively, and were evaluated using the TopSpin 2.1 software package; chemical shifts were determined using the central peak of the solvent. Column chromatography purifications were performed under “flash” conditions using Merck 230–400 mesh silica gel (Darmstadt, Germany). Thin layer chromatography was carried out on Merck silica gel 60 F254 plates, which were visualized by exposure to ultraviolet light and to an aqueous solution of ceric ammonium molybdate.

Chemicals were used without further purification and bought from common commercial suppliers (Sigma‐Aldrich, Milan, Italy and Alfa Aesar, Karlsruhe, Germany). Melting points were determined on a Büchi B‐545 apparatus (Büchi Labortechnik AG Flawil, Switzerland) and are uncorrected. By combustion analysis (C, H, N) carried out on a Carlo Erba Model 1106‐Elemental Analyzer, we determined the purity of synthesized compounds; the results confirmed a ≥95 % purity. Merck Silica Gel 60 F254 plates were used for analytical thin‐layer chromatography (TLC; Merck KGaA, Darmstadt, Germany). For detection UV light (254 nm) was used. ¹H NMR spectra and ¹³C NMR spectra were measured in dimethylsulfoxide‐d6 (DMSO‐d₆) with a Varian Gemini 500 spectrometer (Varian Inc. Palo Alto, California USA); chemical shifts are expressed in δ (ppm) and coupling constants (J) in hertz (Hz). All exchangeable protons were confirmed by addition of D₂O. R_f values were determined on TLC plates using a mixture of CH₂Cl₂/CH₃OH (96 : 4) as eluent.

All reactions were carried out in closed glass vessels under atmospheric pressure without special need for an inert atmosphere. Unless otherwise stated, there was no need for special precautions to exclude moisture. Reagents and solvents were used as purchased without further purification. Proton and carbon NMR spectra for all compounds were acquired on a Bruker Avance III HD 400 MHz spectrometer (Bruker Switzerland AG, Faellanden, Switzerland) at room temperature. Chemical shifts were directly referenced to the residual non-deuterated solvent signal. Ion Chromatography (IC) was performed on a Dionex ICS-2000 System (Thermo Fisher Scientific AG, Reinach, Switzerland). Thin layer chromatography was performed using Merck silica gel 60 F254 plates (Merck KGaA, Darmstadt, Germany) with a solvent system n-butanol/water/acetic acid 5:3:2 and visualized with UV light. Melting points (Mp) were measured on a Büchi B-540 melting point apparatus (Büchi Labortechnik AG, Flawil, Switzerland). The synthetic procedures are reported in the Supplementary Information.

Commercial reagents, all organic solvents and water (HPLC grade), formic acid (95–97%, Laboratory grade), and ammonium formate (AR grade) were purchased from Sigma–Aldrich (Steinheim, Germany).
TLCs were run on Merck silica gel 60 F254 plates (Kenilworth, NJ, USA) and the spots were visualized by means of a UV lamp (Vilber Lourmat VL-4LC, 365 and 254 nm). Silica gel chromatography was performed using Merck silica gel 60 (0.063–0.200 mm). UV experiments were performed on a JASCO V-530 spectrophotometer, equipped with a PTC-348 temperature controller. ¹H (500 MHz and 400 MHz) and ¹³C (125 MHz and 100 MHz). NMR spectra were recorded on an Agilent INOVA spectrometer (Agilent Technology, Cernusco sul Naviglio, Italy) [34 (link),35 (link),36 (link)]; chemical shifts were referenced to the residual solvent signal (CD₃OD: δ_H = 3.31, δ_C = 49.0 ppm, CDCl₃: δ_H = 7.26, δ_C = 77.0 ppm). For an accurate measurement of the coupling constants, the one-dimensional ¹H NMR spectra were transformed at 64 K points (digital resolution: 0.09 Hz). ¹H connectivities were determined by COSY (mixing time 100 ms).