Directdrive nmr system

Melting point determination was performed on a PTP-M apparatus (Khimlabpribor, Klin, Russia). The infrared (IR) spectrum was recorded in CHCl₃ on a Specord 75IR spectrometer (Analytik Jena, Jena, Germany) and the ultraviolet (UV) spectrum was recorded in EtOH on a Beckman Coulter DU 800 spectrometer (Beckman Coulter Inc., Brea, CA, USA). ¹H and ¹³C nuclear magnetic resonance (NMR) spectra were recorded on a Varian DirectDrive NMR System (Varian, Palo Aho, CA, USA) in CDCl₃ at 700 and/or 175.8 MHz. CDCl₃ was used as an internal standard. Mass spectrometry with electrospray ionization MS (ESI) was performed using LC-MS high-resolution spectrometer MaXis (ESI-QTOF) (Bruker Corporation, Billerica, MA, USA), with direct injections of sample solutions into the ionization chamber. X-ray diffraction was measured on Kappa Apex II device (Bruker Corporation, Billerica, MA, USA) by use of CuKα radiation (λ = 1.54178 Å). Intensity of reflexes was integrated and scaled by means of the Saint and Sadabs programs from an Apex II package (Bruker AXS Inc., Madison, WI, USA). All subsequent procedures for the decision and specification of the compound structure were held in the software package of Olex2 (https://www.olexsys.org/olex2/, accessed on 1 January 2020) [44 (link)].

One-dimensional (¹H, ¹³C) and two-dimensional (HSQC, HMBC, H2BC) NMR spectra were recorded on a DirectDrive NMR System (Varian, Palo Aho, CA, USA) in D₂O at 700 and/or 175.8 MHz. The residual signals of H₂O (for ¹H NMR), as well as of CH₃OH (for ¹³C NMR) which was introduced as a micro-impurity in one of the experiments, were used as internal standards.