Synthesis and Characterization of Betulinic Acid Derivatives

All commercial reagents were purchased from Sigma-Aldrich and Acros organics (Verona, Italy). Betulinic acid was prepared from commercially available betulin by a reported procedure [16 (link)]. All commercially available solvents and reagents used were of analytical grade and without further purification. Reactions were monitored by TLC on Sorbfil plates. Column chromatography was carried out on Acrus silica gel (0.060–0.200 mm). Optical rotations were measured on a Perkin–Elmer 341 polarimeter (Waltham, MA, USA). Melting points were recorded on Stuart SMP3. IR spectra were recorded on Bruker VERTEX 70 V using KBr discs over the range of 400–4000 cm⁻¹ (Billerica, MA, USA). ¹H and ¹³C NMR spectra were obtained using a Bruker Ascend 500 spectrometer in CDCl₃ operating at 500 MHz for ¹H and 125 MHz for ¹³C and a Bruker AVANCE 400 spectrometer in CDCl₃ operating at 400 MHz for ¹H and 100 MHz for ¹³C. Mass spectra of MALDI TOF/TOF positive ions (matrix of sinapic acid) are recorded on a mass spectrometer Bruker AutoflexTM III Smartbeam. Elemental analyses were measured on 1106 Carlo Erba apparatus (Val de Reuil, France). Figures S1–S99 show the ¹H and ¹³C NMR spectra of the synthesized compounds.