## 1 Introduction  
Compounds derived from plants or other organisms are characterized by diverse structures and a broad range of biological activities, including antiviral properties [1; 2; 3; 4; 5; 6]. Viruses and viral diseases have been at the center of interest of researchers in the field of medicine and agriculture for decades. Viral infections in humans and animals are the cause of various acute and chronic diseases. Regardless of significant medical progress, such as the development of many vaccines, there are still viral diseases, such as acquired immunodeficiency syndrome (AIDS), respiratory syndromes (severe acute respiratory syndrome--SARS; Middle East respiratory syndrome--MERS; or coronavirus disease 2019--COVID-19) and inflammation of the liver (hepatitis A, B and C), which are causes of high mortality [7; 8; 9]. Viruses also cause serious diseases of plants (e.g., tobacco mosaic virus, tomato yellow leaf curl virus, plum box virus, and potato virus Y) and livestock (e.g., foot and mouth disease, rabies, rinderpest, bovine viral diarrhea, equine influenza, African swine fever, and avian influenza), negatively affecting agriculture and the livestock industry [2; 10; 11; 12]. Many families of viruses have been characterized, differing in the type of nucleic acid, virulence and type of diseases caused in humans. Among them, there are adeno-viruses responsible for viral conjunctivitis, keratitis and respiratory infections or herpesviruses that cause cold sores, chickenpox, shingles, and Kaposi's sarcoma [13]. Mild col infections (e.g., SARS, MERS, or COVID-19) are caused mostly by the coronavirus family or respiratory influenza virus belonging to the orthomyxoviruses [9; 14]. Papillomaviruses are the cause of warts on the skin and also cervical cancer [15]. Picornaviruses from the rhinovirus group cause, among other conditions, colds, and hepatoviruses cause hepatitis A [16]. Smallpox virus belongs to the group of poxviruses and the rabies virus, which can be transmitted to humans by animals, belongs to rhabdomyuses [17]. Retroviruses are also an important group--they have the ability to carry out the reverse transcription process, which allows them to integrate their DNA with the host genome and create latent reservoirs of viruses, e.g., the human immunodeficiency virus (HIV) responsible for AIDS [7; 18]. Viruses show different strategies for invading the body's cells due to their genetic variability, the unique structure of molecular surface, and the course of the replication process. The unique nature of viruses poses challenges in implementing effective antiviral chemotherapy. Therefore, there is a continuous quest for novel antiviral agents characterized by optimal potency, selectivity, in vivo stability, and minimal toxicity. The reduction in conventional drugs used to treat viral infections and the emergence of specific viral resistance has increased the interest in plant-derived antivirals [19]. Tritrepenoids play an important role in plant defense mechanisms against infections caused by various pathogens. The antiviral activity of triterpenoids is often associated with preventing virus adsorption and invasion into the host cells at an early stage. This leads to an inhibition of the viral replication process after the cell is infected [20]. Betulin and betulinic acid (Figure 1) belonging to the lupane-type pentacyclic triterpenes isolated from the bark of _Betulaceae_ family have significant potential as antiviral agents [21]. The search for natural plant products as anti-AIDS agents has led to the testing of betulin and betulinic acid for anti-HIV activity. Betulin has been shown to inhibit both HIV-1 replication in H9 lymphocytes with an EC\({}_{50}\) = 23 uM (effective concentration refers to the concentration of the tested substance that induces a protective effect against the virus in 50% of cells) and the growth of uninfected H9 cells with an IC\({}_{50}\) (concentration of compound which is cytotoxic for 50% of cells) value of 45 uM [22].