No abstract

New cyclopropane derivatives of betulin were synthesized by attachment of dichlorocarbenes or dibromocarbenes to the double bond of betulin diacetate, followed by the deprotection of hydroxyl groups. The betulin cyclopropane derivative was obtained from 20,29-dihydro-20,29-dichloromethylenebetulin by treatment with lithium in tert-butanol. These compounds were converted into the corresponding derivatives of betulonic acid by oxidation with chromium trioxide. The reduction of oxo group with sodium borohydride led to the corresponding derivatives of betulinic acid. 20,29-Dihydro-20,29-dichloromethylenebetulinic acid proved to be the most cytotoxic toward human melanoma of the Colo 38 and Bro lines and human ovarian carcinoma of the CaOv line (IC50 10 microM). 20,29-Dihydro-20,29-dibromomethylenebetulinic acid inhibited the growth of the Bro melanoma cell line and the CaOv carcinoma cell line practically by 50% at a concentration of 10 microM. The other derivatives of betulinic and betulonic acids were active toward all of the three cancer cell lines at concentrations higher than 10 microM. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2005, vol. 31, no. 3; see also http://www.maik.ru.

No abstract

Lake Sevan, Armenia, is the largest freshwater body in the Caucasus region. Cyanobacteria have become increasingly dominant in summer in Lake Sevan, reflecting the eutrophication of the lake and formed a massive bloom event in 2018. These recent observations mark the transition of this previously oligotrophic high mountain lake into an eutrophic lake with scum-forming cyanobacterial blooms. A bloom of Dolichospermum in July caused a sudden increase in chlorophyll-a concentrations up to, on average, 20 µg/L and a strong decrease in water transparency. The cyanobacterial genera Dolichospermum, Aphanizomenon, Anabaena, Cyanobium, and Synechococcus were detected by metagenomic analysis of the lake bacterioplankton. A qualitative and quantitative assessment of peptide-based secondary metabolites revealed the first detection of cyanotoxins in Lake Sevan. Ten types of microcystin congeners were found in Lake Sevan. The total concentration of microcystins in the phytoplankton varied from 0.34 to 2.49 µg/L. This first record of cyanotoxins in the largest lake in the Caucasus region calls for an urgent need for sustainable nutrient management and a systematic assessment of the ultimate causes that lead to the reoccurrence of scum-forming Cyanobacteria in this large Alpine lake.