Ammonium hydroxide solution 25 nh3 h2o

Unless otherwise specified, all reagents and materials used were obtained without additional purification from commercial suppliers. Betulinic acid (BA) (≥98%), 1-octanol, and acetonitrile (for HPLC, gradient grade) were obtained from Sigma-Aldrich (Steinheim am Albuch, Germany). L-aspartic acid, L-isoleucine, L-leucine, L-methionine, L-proline, L-threonine, and L-valine of purity ≥98% were purchased from FluoroChem (Derbyshire, UK). L-serine (≥98.5%), L-phenylalanine (≥98.5%), L-proline (≥98.5%), and L-cysteine (≥98%) were provided by Carl Roth (Karlsruhe, Germany). L-alanine (>99.0%) was acquired from Bachem (Bubendorf, Switzerland) and L-lysine (≥98.0%, anhydrous) from Glentham Life Sciences (Corsham, UK). L-phenylalanine (99%) was provided by Alfa Aesar (Ward Hill, MA, USA). L-tryptophan (>98.5%) was purchased from TCI. Thionyl chloride (99.5%) was provided by Across Organic Geel (Geel, Belgium). Ammonium hydroxide solution 25% (NH₃.H₂O) of analytical grade was purchased from StanLab (Lublin, Poland). Ethanol (99.8%) was provided by Merck (Darmstadt, Germany). Methylene chloride and DMSO of high purity were provided by Chempur (Gliwice, Poland). Deuterated dimethyl sulfoxide (DMSO-d₆) (99.8%) was obtained from Deutero GMBH (Kastellaun, Germany).

All reagents were commercially available materials and were used without further purification. (+)-(S)-2-(6-Methoxynaphthalen-2-yl)propanoic acid (≥98%) was provided from AmBeed (Arlington Heights, IL, USA). L-proline (≥98.5%) was obtained from Carl Roth (Karlsruhe, Germany). Trimethylsilyl chloride (≥99%) (TMSCl) was purchased from Sigma-Aldrich (Steinheim am Albuch, Germany). Ammonium hydroxide solution 25% (NH₃∙H₂O) was of analytical grade obtained from StanLab (Lublin, Poland). Methanol (MeOH), ethanol (EtOH), propan-2-ol (i-PrOH), propan-1-ol (PrOH), butan-1-ol (BuOH), dimethyl sulfoxide, chloroform, ethyl acetate, diethyl ether, toluene, and n-hexane of high purity were purchased from Chempur (Gliwice, Poland). Deuterated chloroform (CDCl₃) (99.8%) (+0.03% TMSCl) was provided by Eurisotop (Cheshire, England). Acetonitrile was provided by J.T. Baker (Radnor, Pennsylvania, USA). PBS (pH 7.4), potassium dihydrogen phosphate (p.a.) was purchased from Merck (Darmstadt, Germany). For cell culture studies, murine fibroblast cell line, L929, and all cell culture reagents were purchased from Sigma Aldrich (Poznań, Poland), while all sterile, single-use cell culture plasticware was purchased from VWR (Gdańsk, Poland).