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Graphical abstract, Highlights • It is the first report to display structure-anti-DENV activity relationships of Glycyrrhizic acid (GL) derivatives. • GL conjugates with isoleucine 13 and 11-aminoundecanoic acid 17 have been identified as potent DENV2 inhibitors. • GL derivatives 13 and 17 showed lower IC50 values (1.2–1.3 μM) against DENV2 infectivity in Vero E6 cells than GL (IC50 8.1 μM)., Dengue virus (DENV) is one of the most geographically distributed pathogenic flaviviruses transmitted by mosquitoes Aedes sps. In this study, the structure-antiviral activity relationships of Glycyrrhizic acid (GL) derivatives was evaluated by the inhibitory assays on the cytopathic effect (CPE) and viral infectivity of DENV type 2 (DENV2) in Vero E6 cells. GL (96% purity) had a low cytotoxicity to Vero E6 cells, inhibited DENV2-induced CPE, and reduced the DENV-2 infectivity with the IC50 of 8.1 μM. Conjugation of GL with amino acids or their methyl esters and the introduction of aromatic acylhydrazide residues into the carbohydrate part strongly influenced on the antiviral activity. Among compounds tested GL conjugates with isoleucine 13 and 11-aminoundecanoic acid 17 were found as potent anti-DENV2 inhibitors (IC50 1.2–1.3 μM). Therefore, modification of GL is a perspective way in the search of new antivirals against DENV2 infection.

The synthesis of a new group of triterpenoid acylates has been conducted on the basis of oleanolic, glycyrrhetic, and ursolic acids and betulin. 28-ortho-Methoxycynnamoylbetulin has been demonstrated to possess high activity against the influenza type A (H1N1) virus with the selectivity index SI > 100 while studying the activity of the synthesized compounds in relation to the reproduction of viral pathogens of respiratory infections. The high activity of 3,28-dinicotinoylbetulin against the papilloma virus (strain HPV-11) was detected with the selectivity index SI 35.

The first example of aza-Michael reaction of 12-N-carboxamide of quinolizidine alkaloid (–)-cytisine with α,β-unsaturated ketones, dimethyl acetylenedicarboxylate and β-nitrostyrene under high pressure condition has been described. It has been shown that the [4+2]-cycloaddition takes place in the case with N-phenylmaleimide.

The oxidative decarboxylation of betulonic, 3,20-dioxo-29- nor-lupan-28-oic, dihydrobetulonic acids with Pb(OAc)4 in the presence of Py, Cu(OAc)2, CF3COOH or with PhI(OAc)2 – I2 leads to 28- nor-lup-16(17)-enes and 28- nor-lup-17(22)-enes, and 17α-acetoxy derivatives. The proportion of regioisomeric olefines is related to a substituent at C-19; the yields of olefines and of acetoxy derivatives depends on reaction conditions and structures of the starting acids. The structures of products were determined by spectroscopic methods.

The oxidative transformations of lappaconitine and 19-oxolappaconine were studied. The product of oxidation of the latter with K2Cr2O7/30% H2SO4 in methylene chloride was proved to be 10,12-dihydro-8,9-seco-19-oxolappaconine in contrast to the earlier proposed structure of this compound.

On the basis of chemical reactions and spectroscopy, it has been shown that the new alkaloid iliensine has the lycoctonine skeleton with α-hydroxy groups at C3 and C10, an α-glycol system at C7–8, β-methoxy group at C6 and C15, a methoxymethyl group at C4, and an iminoethyl group. A correlation has been made of iliensine with acomonine.

The structure of talatisamine has been established by a study of the products of the pyrolysis of diacetyltalatisamine and of the NMR and mass spectra of talatisamine and its conversion products.