Binding of cholera toxin B-subunits to derivatives of the natural ganglioside receptor, GM1.

In a previous paper we showed that the B-pentamer of cholera toxin (CT-B) binds with reduced binding strength to different C(1) derivatives of N-acetylneuraminic acid (NeuAc) of the natural receptor ganglioside, GM1. We have now extended these results to encompass two large amide derivatives, butylamide and cyclohexylmethylamide, using an assay in which the glycosphingolipids are adsorbed on hydrophobic PVDF membranes. The latter derivative showed an affinity approximately equal to that earlier found for benzylamide ( approximately 0.01 relative to native GM1) whereas the former revealed a approximately tenfold further reduction in affinity. Another derivative with a charged C(1)-amide group, aminopropylamide, was not bound by the toxin. Toxin binding to C(7) derivatives was reduced by about 50% compared with the native ganglioside. Molecular modeling of C(1) and C(7) derivatives in complex with CT-B gave a structural rationale for the observed differences in the relative affinities of the various derivatives. Loss of or altered hydrogen bond interactions involving the water molecules bridging the sialic acid to the protein was found to be the major cause for the observed drop in CT-B affinity in the smaller derivatives, while in the bulkier derivatives, hydrophobic interactions with the protein were found to partly compensate for these losses.     

Mass spectrometry and chromatography of t-butyldimethylsilyl derivatives of cytokinin bases

Di-(t-butyldimethylsilyl) derivatives of the cytokinin bases zeatin, cis-zeatin, and dihydrozeatin may be prepared quantitatively in the presence of dimethylaminopyridine. These derivatives have good gas chromatographic properties and are very suitable for gas chromatography-mass spectrometry analysis of cytokinin bases. The t-butyldimethylsilyl (tBuDMS) group at N-9 may be selectively hydrolyzed and the resulting mono-O-silyl derivatives are sufficiently stable to be subjected to thin-layer chromatography and high-performance liquid chromatography. The mass spectral fragmentation of the mono- and di-tBuDMS derivatives of adenine, zeatin, cis-zeatin, and dihydrozeatin and also of the mono-tBuDMS derivatives of N6-isopentenyladenine and 6-benzylaminopurine have been rationalized. The 9-tBuDMS moiety was characterized by an elimination of isobutene (M-56) and of isobutene plus a methyl radical (M-56-15).     

Synthetic Studies on Cyclopentane Derivatives

Reactions of enol ethers of cyclopentane-1,3-dione derivatives (I) with cyanide ion were investigated in order to develope new synthetic routes to 3-functionalized-2-cyclopenten-1-one derivatives from I.

I could be converted to the 3-cyano-2-cyclopenten-1-one skeleton by several procedures for hydrocyanation, among which Nagata’s reagents (HCN-triethylaluminium, diethylaluminium cyanide) were proved to be potent ones.

Reactions of enol ethers of 4-hydroxy-cyclopentane-1,3-dione derivatives were also investigated. From 4-hydroxy-3-methoxy-2-cyclopenten-1-one derivatives (V) 1,4-addition type products with the 4-hydroxy-3-cyano-2-cyclopenten-1-one skeleton (VIII) were obtained as sole isolatable products. NMR studies of some hydroxy-cyclopentenone derivatives were also described.     

Gas-liquid chromotography of trimethylsilyl and alkyl oxime-trimethylsilyl derivatives of some prostaglandins

TMS (trimethylsilyl), MO-TMS (methyl oxime-TMS), and EO-TMS (ethyl oxime-TMS) derivatives of several prostaglandins (A, B1, B2, E1, 8-iso-E1, E2 and 8-iso-E2) were prepared and their gas chromatographic properties examined on a moderately polar (OV-17) and a relatively non-polar (SE-30) stationary phase. Combined gas chromatography-mass spectrometry (GC-MS) using an LKB 9000 instrument was used to identify the different derivatives. Although the TMS derivatives are more easily prepared, the TMS derivatives of the PgE series are thermally somewhat unstable. Thus, MO-TMS and EO-TMS derivatives which exhibit more regular retention increments are more useful for analytical work. The EO-TMS derivatives may be useful in determining mass spectral fragmentation modes of the prostaglandin derivatives.     

Theoretical investigation of the two-photon absorption properties of 3,6-bis(4-vinylpyridinium) carbazole derivatives—new biological fluorescent probes

The present study focuses on a series of carbazole derivatives, which are being investigated as potential two-photon fluorescent probes (TFP) for DNA detection and two-photon bioimaging. The geometric structures, electronic structures, and the one-photon (OPA) and two-photon (TPA) absorption properties of 3,6-bis(1-methyl-4-vinylpyridinium) carbazole (BMVC) derivatives, as well as their dications and diiodized derivatives, were studied using density functional theory (DFT) and Zerner's intermediate neglect of differential overlap (ZINDO) method. The results showed that the TPA spectra of the diiodized BMVC derivatives and their dications are all found in the near-infrared region (NIR). At the same time, the diiodized BMVC derivatives presented larger TPA cross-sections than the neutral BMVC derivatives and the dications. These theoretically derived values were also in good agreement with their corresponding experimentally observed values, and they indicated that the diiodized BMVC may be the form of this TFP that combines with DNA. The diiodized BMVC derivatives and the dications have the potential to be excellent TPA materials, especially when used as TFPs in nucleic acid imaging applications.     

Structural derivatives of pindolol: relationship between in vivo and in vitro potencies for their interaction with central beta-adrenergic receptors

Although (-)-125I-iodopindolol (IPIN) can be used to label beta-adrenergic receptors in the central nervous system (CNS) in vivo, use of this ligand for receptor imaging studies in humans may be limited due to its relatively poor penetration into the CNS. A series of derivatives related to pindolol was therefore studied in an effort to determine the factors that might influence the penetration and interaction of these compounds with central beta-adrenergic receptors in vivo. Evaluation of the ability of these derivatives to displace the binding of IPIN in the brain upon systemic administration provides an assessment of whether the derivatives penetrate and interact with central beta-adrenergic receptors in vivo. Multiple regression analyses showed that the most important factor which influences the ability of the pindolol derivatives to penetrate into the brain and interact with beta-adrenergic receptors in vivo is the affinity of the derivatives for binding to beta-adrenergic receptors in vitro. Both lipophilicity and the molecular weights of the derivatives are important secondary factors which influence their in vivo potency.     

Use of two-dimensional thin-layer chromatography for the components study of poly(adenosine diphosphate ribose)

Two-dimensional thin-layer chromatography on cellulose plates has been used for separating and quantifying the three adenosine derivatives: AMP, phosphoribosyl AMP (PRAMP), and (PR)2AMP obtained by venom phosphodiesterase digestion of poly(ADP-ribose). In vitro synthesized polymer, up to 300 derivatives in length were studied. Some parameters of the complexity of poly(ADP-ribose) could be deduced from our results: (i) The first branching point appears in fragments of approximately 21 derivatives in length. (ii) The branching points are located at regular distances of approximately 41 derivatives from each other.     

Biological activity of bis-benzimidazole derivatives on DNA topoisomerase I and HeLa, MCF7 and A431 cells

Benzimidazoles of both natural and synthetic sources are the key components of many bio-active compounds. Several reports have shown antifungal, antiviral, H(2) receptor blocker and antitumor activities for benzimidazoles and their derivatives. In this study, we synthesized twelve bis-benzimidazole derivatives by selecting di(1H-benzo[d]imidazol-2-yl)methane as the main compound. The numbers of carbons at 2 positions of bis-benzimidazole derivatives were changed from 1 to 4, and derivatives were synthesized with methyl substitutions at 5- and/or 6- positions. The compounds were screened via in vitro plasmid superciol relaxation assays using mammalian DNA topoisomerase I and cytostatic assays were carried out against HeLa (cervix adenocarcinoma), MCF7 (breast adenocarcinoma) and A431 (skin epidermoid carcinoma) cells for selected derivatives. Our results suggest that the malonic acid derivatives of bis-benzimidazoles, namely, bis(5-methyl-1H-benzo[d]imidazol-2-yl)methane and bis(5,6-dimethyl-1H-benzo[d]imidazol-2-yl)methane, were remarkably active compounds in interfering with DNA topoisomerase I and the former compound was also found to be cytotoxic against MCF7 and A431 cells. The inhibitory effects obtained with these derivatives are significant as these compounds can be potential sources of anticancer agents.     

Controllable selective synthesis of a polymerizable prodrug of cytarabine by enzymatic and chemical methods

Selectivity of enzymatic and chemical methods for transesterifications of cytarabine with divinyl dicarboxylates was described. Catalysis by lipase acrylic resin from Candida antarctica (CAL-B) in acetone facilitated the single step synthesis of polymerizable 5'-O-acyl cytarabine derivatives in high yields, while the use of alkaline protease from Bacillus subtilis (subtilisin) in pyridine afforded the mixture products of 5'-O-acyl and 4-N-acyl cytarabine derivatives. Interestingly, polymerizable 4-N-acyl cytarabine vinyl derivatives can be selectively prepared by chemical transesterification in dioxane. The obtained series of cytarabine derivatives would be useful for a significant monomer for a polymeric anticancer drug.     

Synthesis and characterization of folic acid modified water-soluble chitosan derivatives for folate-receptor-mediated targeting

Three chemical modification methods of carboxymethylation, quaternization and hydroxypropylation were used to synthesize water-soluble chitosan derivatives. In order to study the feasibility of these chitosan derivatives as backbones of nuclear imaging agents, folic acid (FA) and Technetium-99m were introduced onto the water-soluble chitosan chains. The bifunctional chelating agent 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) was conjugated to the folate grafted chitosan derivatives for chelating with radionuclides such as (64)Cu and (68)Ga. The structures of these new ligands were characterized with multiple methods. The solubility and stability of the (99m)Tc-complexes were both favorable. Further study of their radiochemical and biological properties will be performed to evaluate the usefulness of these water-soluble chitosan derivatives for nuclear imaging agent design.     

Synthesis of the cyclic and acyclic acetal derivatives of 1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)cytosine,a potent antitumor nucleoside. Design of prodrugs to be selectively activated in tumor tissues via the bio-reduction-hydrolysis mechanism

We have designed and synthesized the acetal derivatives of 1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)cytosine (ECyd, 1), the 2',3'-O-nitrobenzylidene derivatives 2 and 3 and the 5'-O-(alkoxy)(nitrophenyl)methyl derivatives 6-10 as potential prodrugs of ECyd. These prodrugs can be selectively activated in tumor tissues via a bio-reduction-hydrolysis mechanism owing to the characteristic properties of tumor tissues, such as hypoxia and lower pH. Although the 2',3'-O-(4-nitrobenzylidene) derivatives 2 and 3 were converted bio-reductively into the corresponding 4-aminobenzylidene derivatives by rat S-9 mix, the reduction products, that is, the corresponding amino congeners 4 and 5, proved to be rather stable in an aqueous solution at pH 6.5 used as a pH model for acidic tumor tissues. In contrast, the 5'-O-(alkoxy)(4-nitropheny)methyl derivatives 6-8 were also reduced by rat S-9 mix to the corresponding amino congeners 11-13, which were hydrolyzed to release ECyd more effectively at pH 6.5 than at pH 7.4. Accordingly, the acyclic acetals 6-8 may be efficient prodrugs of ECyd, that are effectively reduced under physiological conditions releasing ECyd in acidic tumor tissues.     

Theoretical investigation of the radical scavenging activity of shikonin and acylshikonin derivatives

The radical scavenging activity of shikonin and acylshikonin derivatives was studied by using density functional theory. The hydrogen bond property of the studied structures was investigated using the atoms in molecules (AIM) theory. It turned out that the hydrogen bond is important for good radical scavenging activity. The hydrogen atom transfer for shikonin and acylshikonin derivatives is difficult to obtain because of the high bond dissociation energy (BDE). However, shikonin and acylshikonin derivatives appear to be good candidates for the one-electron-transfer. The introduction of acyl groups for shikonin decreases the ionization potential (IP) values compared with that of shikonin. The acylshikonin derivatives with 1H-pyrrole, furan, and thiophene groups are expected to be of the highest radical scavenging activity among the compounds investigated in this study. Taking this system as an example, we present an efficient method for the investigation of radical scavenging activity from theoretical point of view.     

Potential approaches to prevent uncommon hemolytic side effects of AB0 antibodies in plasma derivatives.

Since hemolytic reactions in patients after administration of plasma derivatives like immunoglobulins or coagulation factor preparations have been described, titers of anti-A and anti-B-antibodies have to be below defined levels for batch release of these plasma-derived therapeutic products according to the European Pharmacopoeia. We have summarized clinical relevance of AB0 antibodies in plasma derivatives and related legal issues in the European Union, United States of America, and Japan. We have also discussed potential approaches for the prevention of hemolytic side effects with feasible steps in preparation of plasma derivatives, viz., (1) selection of donors, (2) exclusion of "dangerous donors", (3) optimizing ratio of the types of plasma, (4) removal of antibodies, (5) production of blood-group-specific plasma derivatives, (6) rejection of batches of plasma derivatives with high titers of antibodies, and (7) crossmatching before administration. For harmonization of standards for anti-A and anti-B in plasma-derived therapeutics the regulators and manufacturers will have to realistically deal with complex clinical, practical, and economic issues.     

Synthesis and CYP24 inhibitory activity of 2-substituted-3,4-dihydro-2H-naphthalen-1-one (tetralone) derivatives

The synthesis of novel 2-benzyl- and 2-benzylidene-3,4-dihydro-2H-naphthalen-1-one (tetralone) derivatives and their inhibitory activity versus kidney mitochondrial 25-hydroxyvitamin D(3) 24-hydroxylase (CYP24) is described. The 2-benzylidenetetralone derivatives were found to be very weak inhibitors (IC(50) 20 >100 microM), whereas the 2-benzyltetralone derivatives showed promising inhibitory activity (IC(50) 0.9 microM for the most active derivative) compared with ketoconazole (IC(50) 20 microM).     

1H, (13)C, and (15)N NMR stereochemical study of cis-fused 7a(8a)-methyl and 6-phenyl octa(hexa)hydrocyclopenta[d][1,3]oxazines and [3,1]benzoxazines

Four 7a-methyl octa(or hexa)hydrocyclopenta[d][1,3]oxazines, five 8a-methyl octa(or hexa)hydro[3,1]benzoxazines, two 6-phenyl hexahydro[3,1]benzoxazinones, and 8a-methyl hexahydro[1,3]benzoxazinone, all cis-fused, were prepared and their stereostructures studied by various one- and two-dimensional (1)H, (13)C, and (15)N NMR spectroscopic methods. In solution, the cyclopentane-fused 2-oxo derivatives and the 1,3-benzoxazinone were found to attain exclusively the N-in/O-in conformation, whereas the 6-phenyl 2-oxo/thioxo derivatives were found to be present predominantly in the N-out conformation. The C-2 unsubstituted and the 2-oxo/thioxo 7a/8a-methyl derivatives were all present in solution as a rapidly interconverting equilibrium of the N-in and N-out conformations. The C-2 methyl derivatives were each found to be interconvertable mixtures of epimers (at C-2) with the N-in conformer predominating for one epimer and the N-out conformer predominating for the other, with both predominating conformers having the C-2 methyl group equatorially orientated. The substituent on the nitrogen (H or Me) was found to be always predominantly equatorial with respect to the heteroring, except for the epimeric 2-methyl derivatives with N-out conformations where steric constraints and the generalized anomeric effect resulted in the axial orientation of the C-2 methyl being favored.     

Hydrophobic derivatives of 2-amino-2-deoxy-D-glucitol-6-phosphate: a new type of D-glucosamine-6-phosphate synthase inhibitors with antifungal action

Several N-acyl and ester derivatives of 2-amino-2-deoxy-D-glucitol-6-phosphate (ADGP) have been synthesised and tested as inhibitors of fungal enzymes involved in early steps of chitin biosynthesis and for antifungal activity. All the tested derivatives were found to be much poorer inhibitors of the enzyme, D-glucosamine-6-phosphate (GlcN-6-P) synthase, than the parent compound but some of them exhibited much better antifungal activity. MIC values for the investigated compounds ranged between 10 mg mL(-1), found for ADGP and 0.3 mg mL(-1) for the most active derivative, namely ADGP dimethyl ester. Increased affinity of ADGP derivatives to the artificial immobilised cell membrane was correlated with their enhanced ability to be taken up by fungal cells by free diffusion. It was found that some of the examined derivatives behaved as 'pro-drugs' and after internalisation were converted into ADGP in the cell-free extract. This conversion was relatively rapid for ADGP esters but very slow for N-acyl derivatives. Results of our studies demonstrate a possibility of design and preparation of GlcN-6-P synthase inhibitors exhibiting antifungal activity.     

Complementary addressed modification of plasmid DNA

The possibility to accomplish the sequence-specific chemical modification of superhelical DNA with reactive oligonucleotide derivatives was demonstrated. Plasmids containing fragments of the immunoglobulin gene were modified with alkylating derivatives of oligonucleotides complementary to a nucleotide sequence in the immunoglobulin gene. In contrast to the relaxed plasmid DNAs, superhelical DNAs (sigma = -0.1) were found to be attacked by the derivatives at the target nucleotide sequence. The efficiency of the reaction increases with the increase of the plasmids negative superhelicity. It was found also that the denatured derivatives. The sequence-specific modification of plasmid DNAs with the reactive oligonucleotide derivatives can be used for the site-directed mutagenesis and the investigation of the repair processes.     

Photoinduced electron-transfer kinetics of singly labeled ruthenium bis(bipyridine) dicarboxybipyridine cytochrome c derivatives

Cytochrome c derivatives labeled at specific lysine amino groups with ruthenium bis(bipyridine) dicarboxybipyridine [RuII(bpy)2(dcbpy)] were prepared by using the procedure described previously [Pan, L. P., Durham, B., Wolinska, J., & Millett, F. (1988) Biochemistry 27, 7180-7184]. Four additional singly labeled derivatives were purified, bringing the total number to 10. These derivatives have a strong luminescence emission centered at 662 nm arising from the excited state, RuII*. Transient absorption spectroscopy was used to directly measure the rate constants for the photoinduced electron-transfer reaction from RuII* to the ferric heme group (k1) and for the thermal back-reaction from the ferrous heme group to RuIII (k2). The rate constants were found to be k1 = 14 X 10(6) s-1 and k2 = 24 X 10(6) s-1 for the derivative modified at lysine 72, which has a distance of 8-16 A between the ruthenium and heme groups. Similar rate constants were found for the derivatives modified at lysines 13 and 27, which have distances of 6-12 A separating the ruthenium and heme groups. The rate constants were significantly slower for the derivatives modified at lysine 25 (k1 = 1 X 10(6) s-1, k2 = 1.5 X 10(6) s-1) and lysine 7 (k1 = 0.3 X 10(6) s-1, k2 = 0.5 X 10(6) s-1), which have distances of 9-16 A. Transients due to photoinduced electron transfer could not be detected for the remaining derivatives, which have larger distances between the ruthenium and heme groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Synthesis and radioiodination of some daunorubicin and doxorubicin derivatives

Daunorubicin and doxorubicin are efficient agents for cancer treatment. Their clinical efficacy is, however, hampered by their indiscriminant toxicity. This problem may be circumvented by encapsulating the drugs in liposomes and selectively targeting the tumor cells using tumor targeting agents. Furthermore, the antitumor effect could be enhanced by attaching the Auger electron emitter, (125)I, to daunorubicin and doxorubicin derivatives. In this context a number of ester, amide, and amine derivatives of daunorubicin and doxorubicin were synthesized. Benzoic acid ester derivatives of daunorubicin were synthesized by nucleophilic esterification of the 14-bromodaunorubicin with the potassium salt of the corresponding benzoic acid, resulting in good yields. Nicotinic acids and benzoic acids, activated with a succinimidyl group, were coupled to the amino group of daunorubicin to give the corresponding amide derivatives. Amine derivatives were obtained by the reductive amination of aromatic aldehydes with daunorubicin hydrochloride. The stannylated ester and amide derivatives were used as precursors for radioiodination. Radiolabeling with (125)I was performed using chloramine-T as an oxidant. The optimized labeling resulted in high radiolabeling yields (85-95%) of the radioiodinated daunorubicin and doxorubicin derivatives. Radioiodination of the amines was conducted at the ortho position of the activated phenyl rings providing moderate radiochemical yields (55-75%).