RESUMEN
The extract of the White Sea sponge Halichondria panicea (Pallas, 1766) exhibits cytotoxic and cytostatic effects. The main part of the extract consists of hydrophilic low molecular weight compounds: free amino acids (13.9%), glucose (19.9%), polyatomic alcohols (glycerin and others) (6.1%), carboxylic acids (0.7%) and nitrogenous heterocycles (1.2%). Of the substances specific to the metabolome, bicyclic diketopiperazines (four derivatives), pyroglutamic acid, phenylacetic acid, and two steroids (3ß,5α)cholest-7-en-3-ol and dihydrocholesterol were identified. Toxicants characteristic of the genus Halichondria were not found in the White Sea sponge.
RESUMEN
New stereoselective methods for the chemical modification of cytisine based on T-reactions are reported. A reaction of cytisine with 2-chloro-5-nitrobenzaldehyde and followed condensation with 1,3-dimethylbarbituric acid affords N-(5-nitro-2-{1,3-dimethylperhydropyrimidine-2,4,6-trione-5-methynyl})cytisine, which undergoes a cyclization with the tetrahydropyridine ring closure. The cyclization proceeds via two competing routes yielding 5,5-spirobarbituric acid derivatives with 11,19-diaza-pentacyclo[11.7.1.02,11.05,10.014,19]henicosane and 11,15-diazapentacyclo-[11.7.1.02,11.05,10.015,20]henicosane skeletons. The cyclization reaction in solutions afford either 24.25-trans and 15,16-trans isomers or trans and cis isomer mixtures, depending on the specific solvent. Meanwhile, 24,25-cis and 15,16-cis isomers are formed stereoselectively under heterogeneous conditions in water suspensions. Trans-5,5-spirobarbiturates under similar conditions undergo isomerization into more stable cis-analogs by the configuration inversion at the C7 atom. The synthesized 5,5-spirobarbituric acid derivatives were successfully converted into alkaloid-like quinolizidine systems (1R,2R,3R,13S)-7-nitro-18-oxo-11,19-diazapentacyclo[11.7.1.02,11.05,10.014,19]henicosa-5(10),6,8,14,16-pentaene-3-carboxylic acid and (1R,2S,3S,13S)-nitro-16-oxo-11,15-diazapentacyclo[11,7,1.02,11,05,10,015,20]henicosa-5,7,9,17,19-pentaene-3-carboxylic acid and their derivatives via the spiropyrimidine moiety removal by the stereoselective hydrolysis. The molecular and crystal structures of the target substances were elucidated by X-ray crystallography and NMR.