Rearrangements of the Betulin Core. Synthesis of Terpenoids Possessing the Bicyclo[3.3.1]nonane Fragment by Rearrangement of Lupane-Type Epoxides.

The rearrangements of dihydrobetulin, dihydrobetulinic acid, and -lupane epoxides under acidic conditions (HCl, montmorillonite K10, and BF·EtO) were studied. The treatment of dihydrobetulin with HCl or K10 produced -lupane olefins. Their epoxidation afforded epoxides, which, in the presence of protic or Lewis acids, rearranged to dienes or lupanes bearing a bicyclo[3.

Synthesis of bidesmosidic lupane saponins - comparison of batch and continuous-flow methodologies.

Synthesis of lupane bidesmosides was optimized. The title compounds were obtained by glycosylation of 3-O- or 28-O-substituted betulin monodesmosides with Schmidt donors catalyzed by TMSOTf. Classical batch procedure and microreactor technique were used and compared in the above synthesis.

Influence of intramolecular hydrogen bonds on regioselectivity of glycosylation. Synthesis of lupane-type saponins bearing the OSW-1 saponin disaccharide unit and its isomers.

A series of lupane-type saponins bearing OSW-1 disaccharide unit as well as its regio- and stereoisomers were prepared and used for the structure-activity relationships (SAR) study. Unexpected preference for 1→4-linked regioisomers and an unusual inversion of the conformation of the sugar rings were noted. Cytotoxic activity of new lupane compounds was evaluated in vitro and revealed that some saponins exhibited an interesting bioactivity profile against human cancer cell lines.

Circular dichroism and conformational dynamics of cephams and their carba and oxa analogues.

The biological activity of bicyclic beta-lactam antibiotics depends strongly on the absolute configuration of the bridgehead carbon atom. Frelek and co-workers proposed an empirical helicity rule relating the configuration of the bridgehead carbon atom to the sign of the 220 nm band in the electronic circular dichroism (CD) spectrum of beta-lactams. Here we use synthetic organic chemistry, CD spectroscopy, and time-dependent density functional theory (TDDFT) to investigate the validity of this structure-property relationship for eight model compounds.

Synthesis of (3,4) beta-methylenecepham and (3,4) beta-methylene-carbacepham via intramolecular carbene addition to double bond.

A series of new (3,4) beta-methylenecepham and carbacepham analogues were synthesised as potential antibacterial agents. The key step of the synthesis included presumed generation of the carbene species from the oxalimide substrate effected by triethylphosphite and its intramolecular addition to the double bond. The stereochemistry of the tricyclic system has been elucidated by NMR and X-ray crystallography.