*3.2. Instruments*

Ultraviolet (UV) spectra were recorded using a UV 1800 spectrophotometer (Shimadzu USA Manufacturing Inc., Canby, OR, USA) and infrared (IR) spectra were obtained on an Equinox 55 Fourier-transform (FT) IR spectrophotometer (Bruker, Rheinstetten, Germany). HR-ESI-MS experiments were carried out using a Shimadzu hybrid ion trap time-of-flight mass spectrometer (Kyoto, Japan). The operating settings of the instrument were as follows: electrospray ionization (ESI) source potential, −3.8 and 4.5 kV for negative and positive polarity ionization, respectively; drying gas (N2) pressure, 200 kPa; nebulizer gas (N2) flow, 1.5 L/min; temperature for the curved desolvation line (CDL) and heat block, 200 ◦C; detector voltage, 1.5 kV; range of detection, 100–900 *m*/*z*. The mass accuracy was below 4 ppm. The data were acquired and processed using Shimadzu LCMS Solution software (v.3.60.361). The 1H-, 13C-, and two-dimensional (2D) NMR spectra were recorded using NMR Bruker AVANCE III DRX-700, AVANCE DRX-500, and AVANCE DPX-300 instruments (Bruker, Karlsruhe, Germany). The chemical shift values (δ) and the coupling constants (*J*) are given in parts per million and in Hz, respectively. HMBC spectra were optimized for 5 Hz coupling. The key NMR acquisition parameters are shown in the Supplementary Materials.

The X-ray experiments for single crystals were performed using a Bruker SMART-1000 Charge-Coupled Detector (CCD) diffractometer (MoKα-radiation, graphite monochromator). Intensity data were corrected for absorption using the multi-scan method. The structures were solved using the direct methods and refined by the least-squares calculation in anisotropic approximation for non-hydrogen atoms. Hydrogen atoms of ethyl groups after checking their presence in a difference map were placed in geometrically idealized positions and refined in the riding-model approximation. Hydrogen atoms of water molecules and hydroxyl groups were located in the difference Fourier maps and refined with Uiso(H) = 1.5Ueq (O). Data collection and editing, as well as refinement of unit cell parameters, were performed with the SMART [40] and SAINT [41] program packages. All calculations

on the determination and refinement of the structures were carried out using the SHELXTL/PC software [42,43].
