Analytical techniques for determining biotin

Biotin is a vitamin of the B-complex, which plays an important biochemical role in every living cell. In the recent years, the interest in this vitamin has been rekindled, mainly due to its association with serious human disorders, such as the inherited syndrome multiple carboxylase deficiency, which can be successfully treated with biotin administration. Diagnosis of biotin deficiency as well as monitoring of biotin levels in biological fluids of patients receiving biotin treatment is crucial. Equally important is the determination of biotin levels in pharmaceutical preparations as well as in food and food supplement products, which constitute the main source of biotin in humans. Several analytical methods for measuring biotin in various samples, e.g. human fluids, pharmaceutical formulations, food material etc., have been reported in the literature. In this review, the most representative of these methods are presented, and their characteristics are evaluated.     

Pyrrolocarbazole analogs of aromatic skeleton of indolocarbazole natural products

The synthesis of seven pyrrolo[2,3‐a]carbazoles derivatives using Fischer indole cyclization conditions is described. Polyphosphoric acid trimethylsilyl ester was used as a mild catalyst for the cyclization step of intermediate arylhydrazones which were prepared from ethyl 7‐oxo‐4,5,6,7‐tetrahydroindole‐2‐carboxylate and used as such without further purification. In all cases a mixture of two products was obtained, the dihydro and the corresponding dehydrogenated one. The completion of the dehydrogenation was achieved by treatment of this resultant mixture with dichlorodicyanoquinone.     

Modification of Guanine with Photolabile N‐Hydroxypyridine‐2(1H)‐thione: Monomer Synthesis,Oligonucleotide Elaboration,and Photochemical Studies

The photochemistry of N‐hydroxypyridine‐2(1H)‐thione (NHPT), inserted as a photolabile modifier at the 6‐position of 2′‐deoxyguanosine or guanosine, has been evaluated. In particular, 6‐[(1‐oxidopyridin‐2‐yl)sulfanyl]‐ ( 1a ) and 6‐[(pyridin‐2‐yl)sulfanyl]‐2′,6‐dideoxyguanosine ( 2a ), novel photolabile derivatives of the natural nucleosides, were synthesized and characterized. The observed photolysis products of 1a in organic solvents could only be rationalized by assuming a rapid equilibrium with the corresponding 6‐[(2‐thioxopyridin‐1(2H)‐yl)oxy] analogue 3a (Scheme 5). Transient spectroscopy of 1a indicated a strong triplet‐excited state suitable for triplet → triplet energy transfer or singlet‐oxygen generation. The NHPT function was stable enough for (slightly modified) automated solid‐phase oligonucleotide synthesis. The utility of the above compounds is discussed, as well as their potential use in photosensitization of reactive oxygen species in DNA.     

Monitoring of Polycyclic Aromatic Hydrocarbon Levels in Mussels (Mytilus galloprovincialis) from Aquaculture Farms in Central Macedonia Region,Greece, Using Gas Chromatography–Tandem Mass Spectrometry Method

A new sensitive and selective gas chromatography tandem mass spectrometry (GC-MS/MS) method was developed for the analysis of 26 polycyclic aromatic hydrocarbons (PAHs), including 16 Environmental Protection Agency (EPA) and 15 + 1 European Union (EU) PAHs, in mussel samples from aquaculture farms in Thermaikos and Strymonian Gulf, Central Macedonia Region, in three sampling periods. Concentrations were found at moderate to low values at all sampling sites, without exceeding maximum levels set by EU. Low molecular weight PAHs were predominant in all samples. Seasonal variation of the concentrations was observed; values were slightly higher in the winter period. Use of diagnostic ratios for potential sources of PAHs showed both petrogenic and pyrolitic origin. In comparison to other related studies of mussels from the Mediterranean Sea, Greek mussels cultivated in the studied gulfs are low in contaminants due to minimal environmental pollution effects. Low concentrations of PAHs are in compliance with the low values of other POPs which were found in the mussels.     

A novel and efficient method for cleavage of phenacylesters by magnesium reduction with acetic acid

[reaction: see text] In the present study, we use magnesium turnings as a new deprotection reagent for the phenacyl group during orthogonal organic synthesis in the presence of other esters and sensitive protecting groups. By applying the new magnesium turnings/acetic acid deprotection method, phenacyl group can be more easily combined with other protecting groups that are not compatible with the zinc/acetic acid method.     

A systematic investigation of the CuCl2/H2mal/phen reaction system (H2mal = malonic acid): Solution and solid state studies of its products

The systematic investigation of the parameter space of the CuCl₂/H₂mal/phen reaction system in MeOH resulted in the isolation of seven different complexes either as mixtures or in pure form, six of which have been structurally characterized. The molar ratios of the reactants and the crystallization methods have been systematically varied, leading to the isolation of compounds [Cu(H₂O)(phen)(mal)] (1), [Cu(MeOH)(phen)(mal)] (2), [Cu₂Li₂Cl₂(phen)₂(mal)₂(MeOH)₄] (3), [Cu₂(phen)₄(mal)][CuCl(phen)(mal)](OH) (4), [CuCl(phen)₂]Cl (5), and [CuCl(phen)(mal)][CuCl(phen)₂][Cu(phen)₂(Hmal)]Cl (6). The coordination versatility of the malonato ligand has been confirmed by the presence of three different coordination modes and its two deprotonation states in compounds 1–6. Solution studies on methanolic solutions of 2–4 and 6 by mass spectrometry revealed the absence of parent ion peak and the presence of fragment ions of low relative abundance not previously found in their crystal structure, thus indicating decomposition and rearrangement/reorganization of the complexes in solution and confirming the dynamic character of their solutions. Compounds 3 and 4 have been also studied in the solid state by EPR spectroscopy and magnetic measurements.     

Positive effect of natural and negatively charged cyclodextrins on the stabilization of penicillins towards beta-lactamase degradation due to inclusion and external guest-host association. An NMR and MS study

The complexation of penicillin (1a-c) and cephalosporin (2a,b) antibiotics with cyclodextrins (CDs), both natural [beta-CD (3b) and gamma-CD (3c)] and carboxylated [heptakis(6-oxycarbonylethylthio-6-deoxy)-beta-CD sodium salt (4b) and octakis(6-oxycarbonylethylthio-6-deoxy)-gamma-CD (4c) sodium salt], has been studied at neutral pH. Penicillins [ampicillin (1a), amoxicillin (1b) and dicloxacillin (1c) form inclusion complexes with the above CDs, as was shown by extensive NMR spectroscopic studies, whereas cephalosporins (cephalexin, cefadroxil) do not. Inclusion of the penicillins into either 3b or 4b was not accompanied by significant chemical shift changes in the 1H NMR spectra. On the contrary, with the wider 3c and its derivative 4c inclusion was evidenced by both chemical shift displacements of the cavity protons and intermolecular interactions, indicating the formation of primarily 1:1 guest-host inclusion complexes. The binding constants for 1a/3c, 1a/4c and 1c/3c were calculated as 19 +/- 4, 17 +/- 0.9 and 622 +/- 200 M(-1), respectively. With 4c, a 1:2 stoichiometry was also found. In addition, simultaneous formation of aggregates by external association takes place in solution, as shown by the ESI-mass spectrometric data. Studies on the hydrolysis of ampicillin under pseudo-first order conditions using an excess of 3c, 4c and of linear maltoheptaose at pH 7 showed that the drug hydrolysed at a similar rate in all cases. In the presence, however, of beta-lactamase enzyme and the carboxylated host 4c, ampicillin degraded twice as slowly (0.008 h(-1)) as in the presence of beta-lactamase alone (0.017 h(-1)). This was explained by the effective protection provided by both inclusion and external association of the host. The interaction, therefore, of penicillins with carboxylated CDs may present a means to lessen the chemical instability of these drugs in the presence of beta-lactamase enzymes.     

Independent generation of C5'-nucleosidyl radicals in thymidine and 2'-deoxyguanosine

The synthesis of the C5' tert-butyl ketone of thymidine 1a and 2'-deoxyguanosine 2 is achieved by reaction of 5'-C-cyano derivatives with tert-butyl lithium followed by acid hydrolysis. The 5'R configuration is assigned by X-ray crystal structure determination of an opportunely protected derivative of 1a. The (5'S)-isomers of both nucleosides are not stable, and a complete decomposition occurs in the reaction medium. The photochemistry of 1a and 2 effectively produced the thymidin-5'-yl radical and the 2'-deoxyguanosin-5'-yl radical, respectively. In the thymidine system, the C5' radical is fully quenched in the presence of a physiological concentration of thiols. In the 2'-deoxyguanosine system, the C5' radical undergoes intramolecular attack onto the C8-N7 double bond of guanine leading ultimately to the 5',8-cyclo-2'-deoxyguanosine derivative. The cyclization of the 2'-deoxyguanosin-5'-yl radical occurs with a rate constant of ca. 1x10(6) s-1 and is highly stereoselective affording only the (5'S)-diastereomer.