Composition of Lipophilic Components of Rhododendron adamsii Rehd. Ether Extract and Activity against SARS-CoV-2 Main Protease

The composition of the lipophilic components of Rhododendron adamsii Rehd. was studied. Acidic and neutral components were identified by gas chromatography-mass spectrometry. Methyl tert-butyl ether (MTBE), which offers all the advantages of diethyl ether but is free of its disadvantages, was used as the extraction solvent for the raw materials. It does not form peroxides or create increased gas pressure due to its higher boiling point. As a result, comparison with databases allowed identification of triterpenic, phenolcarboxylic, and aliphatic acids with chain lengths of 8 to 30 carbon atoms, including saturated, unsaturated, and dibasic acids. More than 150 triterpenic and aliphatic components of the unsaponifiable residue and acidic fractions were identified. Unsaponifiable residues of lipophilic extracts have previously received almost no research attention. Only components of the essential oils of Rh. adamsii and of other species of the genus Rhododendron have been studied in detail. For bioactivity testing, samples of the whole extract and of its fractions were prepared. Some of the studied samples showed inhibitory activity against the main protease of SARS-CoV-2.