Bohumil Dolensky

Glycol porphyrin derivatives as potent photodynamic inducers of apoptosis in tumor cells.

The design and synthesis of glycol-functionalized porphyrins that contain one to four low molecular weight glycol chains that are linked via ether bonds to the meta-phenyl positions of meso-tetraphenylporphyrin and the comparison of fluorinated and nonfluorinated para derivatives are reported. The cellular uptake and photodynamic activity significantly depend on terminal groups of the glycol substituent. Hydroxy glycol porphyrins, in contrast with methoxy glycol porphyrins, show efficient intracellular transport and a high induction of apoptosis in tumor cell lines in vitro . Furthermore, the ethylene glycol chain at the meta position exhibits a superior efficacy that leads to the permanent ablation of human breast carcinoma (MDA-MB-231) in nude mice. In addition, fluorination enhanced the photosensitizing potential of para-phenyl derivatives. The analysis of the cell-death mechanism revealed that glycol-functionalized porphyrins represent novel nonmitochondrially localized photosensitizers that have a profound ability to induce apoptosis in tumor cells that act upstream of caspase activation. The strong interaction with a tumor marker (sialic acid) indicates the preferential association of these compounds with tumor cells.

Novel heterocyclic Tröger's base derivatives containing N-methylpyrrole units

Abstract Novel analogues of Trogers base were prepared regioselectively from 4-amino- N -methylpyrrole carboxylates in good yield. Catalytic hydrogenation of dibenzyl-4,9-methano-1,6-dimethyl-4,5,9,10-tetrahydro-1 H ,6 H -dipyrrolo-[3,2- b :3′,2′- f ][1,5]diazocin-2,7-dicarboxylate 2b led to 4,9-methano-1,6-dimethyl-4,5,9,10-tetrahydro-1 H ,6 H -dipyrrolo-[3,2- b :3′,2′- f ][1,5]diazocin-2,7-dicarboxylic acid 3 which was used for the preparation of Trogers base derivatives of natural antibiotics via an amide protocol. The novel heterocyclic Trogers bases were characterized by a variety of spectroscopic techniques and compound 2b by X-ray crystallography. Incorporation of guanidine as the terminal group in the N -methylpyrrole Trogers base skeleton opens the possibility for preparation of water soluble derivatives.

Preparation of β-fluoro- and β,β-difluoro-histidinols

Abstract Nucleophilic attack of azide on 2-bromo-3-fluoro-3-(1-trityl-1 H -imidazol-4-yl)-propan-1-ol ( 1a ) in aprotic solvent occurs on the 2-position to give the 2-azido derivative ( 2a ). Reduction of azide and removal of the trityl group produces β-fluorohistidinol ( 6a ). Elimination of HBr from 1a followed by “FBr” addition to the resulting double bond gives 2-bromo-3,3-difluoro-3-(1-trityl-1 H -imidazol-4-yl)-propan-1-ol ( 1b ). Nucleophilic attack of azide followed by reduction and removal of the trityl group, as for the preparation of 6a , gives β,β-difluorohistidinol ( 6b ). Initial attempts, under a variety of conditions, to oxidize the fluorinated histidinol precursors to carboxylic acids have not been successful.

Synthesis of 4,5-difluoroimidazole

Abstract 5-Fluoroimidazole-4-carboxylic acid ethyl ester was converted to the corresponding hydrazide. Oxidation of the hydrazide to the carbonyl azide and Curtius rearrangement in t -butyl alcohol produced 4- t -butyloxycarbonylamino-5-fluoroimidazole. Dissolution of the t -butyl carbamate in 50% HBF 4 , in situ diazotation of the resulting amine, and irradiation produced the target compound.

New approaches to side-chain fluorinated bioimidazoles: 4-alkynylimidazoles as substrates for fluorination

Abstract 4-Alkynylimidazoles have been prepared and their behavior as substrates for “FBr” addition (NBS+Et3N·3HF) have been studied. Facile Markownikov addition to ethylnylimidazole 2 gave fluorobromoolefin 9a, a potential synthon for the 2-imidazolyl-2-fluoro-1-ethenyl moiety. Reaction of the lithium salt of 2 with diethyl oxalate produced imidazolylpropynoic ester 3b. However, because of the deactivating effect of the ester functionality, all attempts to carry out addition of “FBr” to 3b met with failure. Reduction of the ester gave the hydroxymethyl-substituted acetylene 4. Addition of “FBr” to this substrate and reductive removal of bromine from the product produced fluoroolefins 12, precursors to E- and Z-β-fluorourocanic acids. The same fluoroolefins can be used as intermediates in the synthesis of β-fluorohistidinols.

Syntheses of E- and Z-2- and 4-fluorourocanic acids

Abstract Horner–Wadsworth–Emmons olefination of ring-fluorinated N -trityl-imidazole carboxaldehydes with dialkyphosphonoacetic acid esters produced ring-fluorinated imidazolyl- E - and Z -acrylate esters. Stereochemistry was controlled by choice of phoshonate. Acid catalyzed removal of trityl followed by ester saponification gave the target 2- and 4-fluoro- E - and Z -urocanic acid derivatives. These are being investigated as potential mediators of photo-immunosupression.