Spectroscopic Analysis of Usnic Acid Derivatives

The analytical and spectral studies were conducted at the Chemical Service Center for the collective use of Siberian Branch of the Russian Academy of Science. The 1H and ¹³C-NMR spectra for solutions of the compounds in CDCl₃ were recorded on a Bruker AV-400 spectrometer (Bruker Corporation, Hanau, Germany; operating frequencies 400.13 MHz for ¹H and 100.61 for ¹³C). The residual signals of the solvent were used as references (δH 7.27, δC 77.1 for CDCl₃). Merck silica gel (63–200 μ) was used for the column chromatography. Thin-layer chromatography was performed on TLC Silica gel 60F₂₅₄ (Merck KGaA, Darmstadt, Germany). The target compounds reported in this manuscript had a purity of at least 95% (HPLC). All chemicals were used as described unless otherwise noted. Reagent-grade solvents were redistilled prior to use. Synthetic starting materials, reagents, and solvents were purchased from Sigma-Aldrich (St. Louis, MO, USA), Acros Organics (Geel, Belgium), and AlfaAesar (Heysham, UK).
(R)-(+)-Usnic acid (+)-9 was purchased from Zhejiang Yixin Pharmaceutical Co., Ltd. (Lanxi, China). Compounds 3,4 were obtained using a known procedure. The spectra of the substances coincided with that in the literature [31 (link),32 (link)].