A desiccated dual-species subaerial biofilm reprograms its metabolism and affects water dynamics in limestone

Understanding the impact of sessile communities on underlying materials is of paramount importance in stone conservation. Up until now, the critical role of subaerial biofilms (SABs) whether they are protective or deteriorative remains unclear, especially under desiccation. The interest in desiccated SABs is raised by the prediction of an increase in drought events in the next decades that will affect the Mediterranean regions' rich stone heritage as never before. Thus, the main goal of this research is to study the effects of desiccation on both the biofilms' eco-physiology and its impacts on the lithic substrate. To this end, we used a dual-species model system composed of a phototroph and a chemotroph to simulate biofilm behavior on stone heritage. We found that drought altered the phototroph-chemotroph balance and enriched the biofilm matrix with proteins and DNA. Desiccated SABs underwent a shift in metabolism to fermentation and a decrease in oxidative stress. Additionally, desiccated SABs changed the water-related dynamics (adsorption, evaporation, and wetting properties) in limestone. Water absorption experiments showed that desiccated SABs protected the stone from rapid water uptake, while a thermographic survey indicated a delay in water evaporation. Spilling-drop tests revealed a change in the wettability of the stone-SAB interface, which affected the water transport properties of the stone. Finally, desiccated SABs reduced stone swelling in the presence of water vapor. The biodeteriorative and bioprotective implications of desiccated SABs on the stone were ultimately assessed.

Biofilm and Rivers: The Natural Association to Reduce Metals in Waters

This article focuses on a very peculiar habitat, the thin biofilm that covers the surface of rocks, cobbles, sediment grains, leaf litter, and vegetation on a riverbed. Species composition changes over time and depends on environmental conditions and perturbation of water quality. It provides several ecosystem services, contributing to the biogeochemical fluxes and reducing contamination by absorbing the pollutants. Biofilm into the Toce River (Ossola Valley, Piedmont, Italy) was investigated to assess its capacity to accumulate the metals and macroions from the water column. In this preliminary work, we investigated three sample points, in two different seasons. The community composition of biofilm was determined via morphological analysis (diatoms and non-diatoms algal community). We characterize the biofilm, a community of different organisms, from different perspectives. In the biofilm, Hg was analyzed with an automated mercury analyzer, other metals and macroions with inductively coupled plasma mass spectrometry (ICP-MS) (Al, As, Ba, Ca, Cr, Cu, Fe, K, Mg, Mn, Ni, P, Pb, and Zn), and the carotenoid and chlorophyll composition of the photosynthetic organism with HPLC analysis for the primary producers. The results evidence a seasonal pattern in metals and macroions levels in the biofilm, and a significant difference in the biofilm community and in carotenoid composition, suggesting the utility of using the biofilm as an additional bioindicator to monitor the water quality of the river.

Study of alkaloid berberine and its interaction with the human telomeric i-motif DNA structure

The alkaloid berberine presents many biological activities related to its potential to bind DNA structures, such as duplex or G-quadruplex. Recently, it has been proposed that berberine may interact with i-motif structures formed from the folding of cytosine-rich sequences. In the present work, the interaction of this alkaloid with the i-motif formed by the human telomere cytosine-rich sequence, as well as with several positive and negative controls, has been studied. Molecular fluorescence and circular dichroism spectroscopies, as well as nuclear magnetic resonance spectrometry and competitive dialysis, have been used with this purpose. The results shown here reveal that the interaction of berberine with this i-motif is weak, mostly electrostatics in nature and takes place with bases not involved in C·C⁺ base pairs. Moreover, this ligand is not selective for i-motif structures, as binds equally to both, folded structure, and unfolded strand, without producing any stabilization of the i-motif. As a conclusion, the development of analytical methods based on the interaction of fluorescent ligands, such as berberine, with i-motif structures should consider the thermodynamic aspects related with the interaction, as well as the selectivity of the proposed ligands with different DNA structures, including unfolded strands.

Phosphorus speciation during anaerobic digestion and subsequent solid/liquid separation

This study aims to investigate the effect of anaerobic digestion (AD) on P species and how the different species are distributed in the digestate and digestate fractions, i.e. liquid and solid fractions. To do so, six full scale AD plants were used in this work and representative biomass samples were collected for investigation. P fractionation proceeded by adopting fractionation protocols consisting in step-by-step extraction with different solvents, (i.e. NaHCO₃, HCl and NaOH-EDTA). Subsequently P species in the different fractions were identified by using ³¹PNMR. On average, AD did not substantially affect P speciation that depended on the P-fraction content of feeds. A high NaHCO₃ fraction content in the ingestate determined, also, a high content of this fraction in the digestate, with consequently lower contents of both P-HCl and P-NaOH-EDTA, i.e. digestate P-fraction contents represented an inheritance of P speciation in the ingestate. A feed effect was observed in single plants. Highest pig/cow slurry content in the feeds seemed to decrease readily soluble P (extracted with NaHCO₃) content and increased P associated with both organic matter and amorphous Fe/Al in the digestate. Again, using a large amount of digestate in the feed increased P-soluble content in the digestate. ³¹P NMR analyses revealed that inorganic P compounds dominated the spectra of all biomasses and fractions, with orthophosphate as the predominant species. When present, organic phosphorus compounds were typically represented by monophosphate esters, DNA and phospholipids, with a predominance of monophosphate esters.

Stabilization of c-KIT G-Quadruplex DNA Structures by the RNA Polymerase I Inhibitors BMH-21 and BA-41

The stabilization of G-quadruplex DNA structures by small molecules with affinity to oncogene promoters has emerged as a promising anticancer strategy, due to a potential role in gene expression regulation. We explored the ability of BMH-21 (1) and its analogue BA-41 (2) to bind the G-quadruplex structure present in the c-KIT promoter by biophysical methods and molecular modeling. We provide evidence that both compounds interact with the c-KIT 21-mer sequence. The stable monomeric intramolecular parallel G-quadruplex obtained by the mutation of positions 12 and 21 allowed the precise determination of the binding mode by NMR and molecular dynamics studies. Both compounds form a complex characterized by one ligand molecule positioned over the tetrad at the 3′-end, stabilized by an extensive network of π–π interactions. The binding constants (Kb) obtained with fluorescence are similar for both complexes (around 10⁶ M⁻¹). Compound BA-41 (2) showed significant antiproliferative activity against a human lymphoma cell line, SU-DHL4, known to express substantial levels of c-KIT. However, the partial inhibition of c-KIT expression by Western blot analysis suggested that the interaction of compound 2 with the c-KIT promoter is not the primary event and that multiple effects provide a contribution as determinants of biological activity.

Synthesis of a leopolic acid-inspired tetramic acid with antimicrobial activity against multidrug-resistant bacteria

The increasing emergence of multidrug-resistant pathogens is one of the biggest threats to human health and food security. The discovery of new antibacterials, and in particular the finding of new scaffolds, is an imperative goal to stay ahead of the evolution of antibiotic resistance. Herein we report the synthesis of a 3-decyltetramic acid analogue of the ureido dipeptide natural antibiotic leopolic acid A. The key step in the synthetic strategy is an intramolecular Lacey–Dieckmann cyclization reaction of a linear precursor to obtain the desired 3-alkyl-substituted tetramic acid core. The synthesized analogue is more effective than the parent leopolic acid A against Gram-positive (Staphylococcus pseudintermedius) and Gram-negative (E. coli) bacteria (MIC 8 µg/mL and 64 µg/mL, respectively). Interestingly, the compound shows a significant activity against Staphylococcus pseudintermedius strains expressing a multidrug-resistant phenotype (average MIC 32 µg/mL on 30 strains tested). These results suggest that this molecule can be considered a promising starting point for the development of a novel class of antibacterial agents active also against resistant strains.

c-MYC G-quadruplex binding by the RNA polymerase I inhibitor BMH-21 and analogues revealed by a combined NMR and biochemical Approach

BACKGROUND

Pyridoquinazolinecarboxamides have been reported as RNA polymerase I inhibitors and represent a novel class of potential antitumor agents. BMH-21, was reported to intercalate with GC-rich rDNA, resulting in nucleolar stress as a primary mechanism of cytotoxicity.

METHODS

The interaction of BMH-21 and analogues with DNA G-quadruplex structures was studied by NMR and molecular modelling. The cellular response was investigated in a panel of human tumor cell lines and protein expression was examined by Western Blot analysis.

RESULTS AND CONCLUSIONS

We explored the ability of BMH-21 and its analogue 2 to bind to G-quadruplex present in the c-MYC promoter, by NMR and molecular modelling studies. We provide evidence that both compounds are not typical DNA intercalators but are effective binders of the tested G-quadruplex. The interaction with c-MYC G-quadruplex was reflected in down-regulation of c-Myc expression in human tumor cells. The inhibitory effect was almost complete in lymphoma cells SUDHL4 characterized by overexpression of c-Myc protein. This downregulation reflected an early and persistent modulation of cMyc mRNA. Given the relevance of c-MYC in regulation of ribosome biogenesis, it is conceivable that the inhibition of c-MYC contributes to the perturbation of nuclear functions and RNA polymerase I activity. Similar experiments with CX-5461, another RNA polymerase I transcription inhibitor, indicate the same behaviour in G-quadruplex stabilization.

GENERAL SIGNIFICANCE

Our results support the hypothesis that BMH-21 and analogue compounds share the same mechanism, i.e. G-quadruplex binding as a primary event of a cascade leading to inhibition of RNA polymerase I and apoptosis.

Molecular basis for the DNA damage induction and anticancer activity of asymmetrically substituted anthrapyridazone PDZ-7

Anthrapyridazones, imino analogues of anthraquinone, constitute a family of compounds with remarkable anti-cancer activity. To date, over 20 derivatives were studied, of which most displayed nanomolar cytotoxicity towards broad spectrum of cancer cells, including breast, prostate and leukemic ones. BS-154, the most potent derivative, had IC₅₀ values close to 1 nM, however, it was toxic in animal studies. Here, we characterize another anthrapyridazone, PDZ-7, which retains high cytotoxicity while being well tolerated in mice. PDZ-7 is also active in vivo against anthracycline-resistant tumor in a mouse xenograft model and induces DNA damage in proliferating cells, preferentially targeting cells in S and G₂ phases of the cell cycle. Activation of Mre11-Rad50-Nbs1 (MRN) complex and phosphorylation of H2AX suggest double-stranded DNA breaks as a major consequence of PDZ-7 treatment. Consistent with this, PDZ-7 treatment blocked DNA synthesis and resulted in cell cycle arrest in late S and G₂ phases. Analysis of topoisomerase IIα activity and isolation of the stabilized covalent topoisomerase IIα - DNA complex in the presence of PDZ-7 suggests that this compound is a topoisomerase IIα poison. Moreover, PDZ-7 interfered with actin polymerization, thereby implying its action as a dual inhibitor of processes critical for dividing cells. Using nuclear magnetic resonance (NMR) spectroscopy we show that PDZ-7 interacts with DNA double helix and quadruplex DNA structure. Taken together, our results suggest that PDZ-7 is a unique compound targeting actin cytoskeleton and DNA.

Synthesis of the Tripeptide Antibiotic Resormycin

A short and efficient synthesis of resormycin, a metabolite of Streptomyces platensis MJ953-SF5 with herbicidal and antifungal activity, is described. The key step in our synthetic approach is a late-stage stereospecific dehydration of a β-hydroxy amino acid to install the Z-olefin. Because of the modular nature of the synthesis, access to analogues for biological evaluation is readily available.

Total synthesis of leopolic acid A, a natural 2,3-pyrrolidinedione with antimicrobial activity

The first total synthesis of leopolic acid A, a fungal metabolite with a rare 2,3-pyrrolidinedione nucleus linked to an ureido dipeptide, was designed and carried out. Crucial steps for the strategy include a Dieckmann cyclization to obtain the 2,3-pyrrolidinedione ring and a Wittig olefination to install the polymethylene chain. An oxazolidinone-containing leopolic acid A analogue was also synthesized. The antibacterial activity showed by both compounds suggests that they could be considered as promising candidates for future developments.

Nemorubicin and doxorubicin bind the G-quadruplex sequences of the human telomeres and of the c-MYC promoter element Pu22

BACKGROUND

Intra-molecular G-quadruplex structures are present in the guanine rich regions of human telomeres and were found to be prevalent in gene promoters. More recently, the targeting of c-MYC transcriptional control has been suggested, because the over expression of the c-MYC oncogene is one of the most common aberration found in a wide range of human tumors.

METHODS

The interaction of nemorubicin and doxorubicin with DNA G-quadruplex structures has been studied by NMR, ESI-MS and molecular modelling, in order to obtain further information about the complex and the multiple mechanisms of action of these drugs.

RESULTS AND CONCLUSIONS

Nemorubicin intercalates between A3 and G4 of d(TTAGGGT)4 and form cap-complex at the G6pT7 site. The presence of the adenine in this sequence is important for the stabilization of the complex, as was shown by the interaction with d(TTGGGTT)4 and d(TTTGGGT)4, which form only a 1:1 complex. The interaction of doxorubicin with d(TTAGGGT)4 is similar, but the complex appears less stable. Nemorubicin also binds with high efficiency the c-MYC G-quadruplex sequence Pu22, to form a very well defined complex. Two nemorubicin molecules bind to the 3'-end and to the 5'-end, forming an additional plane of stacking over each external G-tetrad. The wild type c-MYCPu22 sequence forms with nemorubicin the same complex.

GENERAL SIGNIFICANCE

Nemorubicin and doxorubicin, not only intercalate into the duplex DNA, but also result in significant ligands for G-quadruplex DNA segments, stabilizing their structure; this may in part explain the multiple mechanisms of action of their antitumor activity.

Molecular recognition in naphthoquinone derivatives - G-quadruplex complexes by NMR

BACKGROUND

G-quadruplexes have become important drug-design targets for the treatment of various human disorders such as cancer, diabetes and cardiovascular diseases. Recently, G-quadruplex structures have been visualized in the DNA of human cells and appeared to be dynamically sensitive to the cell cycle and stabilized by small molecule ligands. A small library of isoxazolo naphthoquinones (1a-h), which exhibited a strong antiproliferative activity on different cancer cell lines, was studied as potential ligands of G-quadruplex DNA.

METHODS

The DNA binding properties of a series of the selected compounds have been analyzed by fluorescence assays. NMR/modeling studies were performed to describe the complexes between G-quadruplex DNA sequences and two selected compounds 1a and 1b.

RESULTS

1a and 1b in the presence of G-quadruplexes, d(T(2)AG(3)T)(4), d(TAG(3)T(2)A)(4) and d(T(2)G(3)T(2))(4), showed good ability of intercalation and the formation of complexes with 2:1 stoichiometry. 1a showed an important interaction with the sequence Pu22 belonging to the promoter of oncogenes c-myc.

CONCLUSIONS

The ligands directly interact with the external G-tetrads of the G-quadruplexes, without alterations in the structure of the G-quadruplex core. The role of the adenine moieties over the G-tetrads in the stabilization of the complexes was discussed.

GENERAL SIGNIFICANCE

The results obtained suggested that the strong antiproliferative activity of isoxazolo naphthoquinones is not due to the Hsp90 inhibition, but mainly to the interaction at the level of telomeres and/or at the level of gene promoter. These findings can be used as a basis for the rational drug design of new anticancer agents.

The interaction of nemorubicin metabolite PNU-159682 with DNA fragments d(CGTACG)(2), d(CGATCG)(2) and d(CGCGCG)(2) shows a strong but reversible binding to G:C base pairs

The antitumor anthracycline nemorubicin is converted by human liver microsomes to a major metabolite, PNU-159682 (PNU), which was found to be much more potent than its parent drug toward cultured tumor cells and in vivo tumor models. The mechanism of action of nemorubicin appears different from other anthracyclines and until now is the object of studies. In fact PNU is deemed to play a dominant, but still unclear, role in the in vivo antitumor activity of nemorubicin. The interaction of PNU with the oligonucleotides d(CGTACG)(2), d(CGATCG)(2) and d(CGCGCG)(2) was studied with a combined use of (1)H and (31)P NMR spectroscopy and by ESI-mass experiments. The NMR studies allowed to establish that the intercalation between the base pairs of the duplex leads to very stable complexes and at the same time to exclude the formation of covalent bonds. Melting experiments monitored by NMR, allowed to observe with high accuracy the behaviour of the imine protons with temperature, and the results showed that the re-annealing occurs after melting. The formation of reversible complexes was confirmed by HPLC-tandem mass spectra, also combined with endonuclease P1digestion. The MS/MS spectra showed the loss of neutral PNU before breaking the double helix, a behaviour typical of intercalators. After digestion with the enzyme, the spectra did not show any compound with PNU bound to the bases. The evidence of a reversible process appears from both proton and phosphorus NOESY spectra of PNU bound to d(CGTACG)(2) and to d(CGATCG)(2). The dissociation rate constants (k(off)) of the slow step of the intercalation process, measured by (31)P NMR NOE-exchange experiments, showed that the kinetics of the process is slower for PNU than for doxorubicin and nemorubicin, leading to a 10- to 20-fold increase of the residence time of PNU into the intercalation sites, with respect to doxorubicin. A relevant number of NOE interactions allowed to derive a model of the complexes in solution from restrained MD calculations. The conformation of PNU bound to the oligonucleotides was also derived from the coupling constant values.

Alkalizing reactions streamline cellular metabolism in acidogenic microorganisms

An understanding of the integrated relationships among the principal cellular functions that govern the bioenergetic reactions of an organism is necessary to determine how cells remain viable and optimise their fitness in the environment. Urease is a complex enzyme that catalyzes the hydrolysis of urea to ammonia and carbonic acid. While the induction of urease activity by several microorganisms has been predominantly considered a stress-response that is initiated to generate a nitrogen source in response to a low environmental pH, here we demonstrate a new role of urease in the optimisation of cellular bioenergetics. We show that urea hydrolysis increases the catabolic efficiency of Streptococcus thermophilus, a lactic acid bacterium that is widely used in the industrial manufacture of dairy products. By modulating the intracellular pH and thereby increasing the activity of β-galactosidase, glycolytic enzymes and lactate dehydrogenase, urease increases the overall change in enthalpy generated by the bioenergetic reactions. A cooperative altruistic behaviour of urease-positive microorganisms on the urease-negative microorganisms within the same environment was also observed. The physiological role of a single enzymatic activity demonstrates a novel and unexpected view of the non-transcriptional regulatory mechanisms that govern the bioenergetics of a bacterial cell, highlighting a new role for cytosol-alkalizing biochemical pathways in acidogenic microorganisms.

Taste-guided identification of high potency TRPA1 agonists from Perilla frutescens

Perilla frutescens is a food plant widely used in Asian cuisine. This plant was investigated for its interesting taste and somatosensory properties. Perillaldehyde and perillaketone are among the components of the aromatic extracts from P. Frutescens. These compounds were shown here to activate the cloned TRPA1 channel when expressed in an heterologous cell system and are therefore suggested to be responsible for the chemesthetic properties of this plant.

Interaction between double helix DNA fragments and a new topopyrone acting as human topoisomerase I poison

A water soluble derivative (2) of topopyrones was selected for NMR studies directed to elucidate the mode of binding with specific oligonucleotides. Topopyrone 2 can intercalate into the CG base pairs, but the residence time into the double helix is very short and a fast chemical exchange averaging occurs at room temperature between the free and bound species. The equilibria involved become slow below room temperature, thus allowing to measure a mean lifetime of the complex of ca. 7 ms at 15 degrees C. Structural models of the complex with d(CGTACG)(2) were developed on the basis of DOSY, 2D NOESY and (31)P NMR experiments. Topopyrone 2 presents a strong tendency to self-associate. In the presence of oligonucleotide a certain number of ligand molecules are found to externally stack to the double-helix, in addition to a small fraction of the same ligand intercalated. The external binding to the ionic surface of the phosphoribose chains may thus represents the first step of the intercalation process.

Conformational study on glycosylated asparagine-oligopeptides by NMR spectroscopy and molecular dynamics calculations

The conformational properties of the homo oligomers of increasing chain length Boc-(Asn)(n)-NHMe (n = 2, 4, 5), (GlcNAc-beta-Asn)(n)-NHMe (n = 2, 4, 5, 8) and Boc-[GlcNAc(Ac)(3)-beta-Asn](n)-NHMe (n = 2, 4, 5) were studied by using NOE experiments and molecular dynamic calculations (MD). Sequential NOEs and medium range NOEs, including (i,i+2) interactions, were detected by ROESY experiments and quantified. The calculated inter-proton distances are longer than those characteristic of beta-turn secondary structures. Owing to the large conformational motions expected for linear peptides, MD simulations were performed without NMR constraints, with explicit water and by applying different treatments of the electrostatic interactions. In agreement with the NOE results, the simulations showed, for all peptides, the presence of both folded and unfolded structures. The existence of significant populations of beta-turn structures can be excluded for all the examined compounds, but two families of structures were more often recognized. The first one with sinusoidal or S-shaped forms, and another family of large turns together with some more extended conformations. Only the glycosylated pentapeptide shows in vacuo a large amount of structures with helical shaped form. The results achieved in water and in DMSO are compared and discussed, together with the effect of the glycosylation.

Unusual accumulation of S-methylmethionine in aerobic-etiolated and in anoxic rice seedlings: an 1H-NMR study

An unknown signal at 2.93 ppm in 1H-NMR spectra of rice, Oryza sativa, was assigned to the methyl groups of sulphur-methylmethionine (SMM), thereby devising a new method for the determination of this compound. Rice seedlings growing aerobically in the dark and in the light engaged for the synthesis of SMM an amount of Met corresponding to 23 and 8%, respectively, of the total seed reserves of this amino acid. In etiolated shoots, SMM reached 1.2 micromol g(-1) fresh weight, an unusually high level in vegetative tissues of wild-type plants. This is compared to a value of 0.4 micromol g(-1) fresh weight in green tissues. A decreased demand for Met during growth caused the higher accumulation of SMM in etiolated, rather than green, tissues. At the same time, dark seedlings were endowed with a readily utilizable and translocable alternative form of Met, as shown by retrieval of SMM from the coleoptile. The importance of methyl group storage in SMM is shown by comparison with choline and choline phosphate pools.

A new 3,4-seco-lupane derivative from Lasianthus gardneri

A new seco-ring A lupane triterpene derivative (1), along with lupenone, lupeol, beta-sitosterol, ursolic acid, and stigmasterol 3-O-beta-d-glucoside, were isolated from a methanol extract of mature stems of Lasianthus gardneri, a shrub from the family Rubiaceae growing in Sri Lanka. The structure and stereochemistry of the new compound were determined using a combination of (13)C and (1)H homo- and heteronuclear 2D NMR experiments and from mass spectral data. The structure of 1 was confirmed by partial synthesis from lupeol.

Neoclerodanes from Teucrium orientale

Two new neoclerodane diterpenoids, 6-deacetyl-teucrolivin A (5) and 8beta-hydroxy-teucrolivin B (6), were isolated from the aerial parts of Teucrium orientale, along with four already known neoclerodane diterpenoids, teucrolivin A (1), teucrolivin B (2), teucrolivin C (3) and teucrolivin H (4), previously isolated from Teucrium oliverianum. Their structures were elucidated on the basis of spectroscopic evidence and chemical transformations. Compounds 1-3 were assayed for antifeedant activity against Spodoptera littoralis, S. frugiperda and Heliocoverpa armigera. Teucrolivin A was the most potent of the three compounds tested.

Structure elucidation of clavilactone D: an inhibitor of protein tyrosine kinases

Clavilactones D and E were isolated from an agar culture of the Basidiomycetous fungus Clitocybe clavipes, and their structure was elucidated by 1H- and 13C-NMR studies. Clavilactone D is an inhibitor of tyrosine kinases.

Reinvestigation of the reaction between 2-furancarboxaldehyde and 4-hydroxy-5-methyl-3(2H)-furanone

The reaction between 2-furancarboxaldehyde and 4-hydroxy-5-methyl-3(2H)-furanone was reinvestigated as a part of a systematic study on low molecular weight colored compounds from the Maillard reaction. In acetic acid/piperidine, besides 2-(2-furanylmethylene)-4-hydroxy-5-methyl-3(2H)-furanone (1) and 5-[2-(2-furanyl)ethenyl]-2-(2-furanylmethylene)-4-hydroxy-5-methyl -3( 2H)-furanone (2), four novel compounds, 15a, 15b, 16a, and 16b, were isolated and characterized. These compounds are produced from two molecules of furanone 1 and one molecule of 2-furancarboxaldehyde, and a mechanism is proposed for their formation. Compounds 1, 15a, 15b, 16a, and 16b are formed also by reacting 2-furancarboxaldehyde and 4-hydroxy-5-methyl-3(2H)-furanone in water at pH 3 and 2, whereas 2 was never detected. The formation of these compounds was studied also in xylose/lysine and xylose/glycine model systems.

Optimization of the synthesis of the cross-linked amino acid ornithinoalanine and nuclear magnetic resonance characterization of lysinoalanine and ornithinoalanine

Lysinoalanine (LAL) and ornithinoalanine (OAL) are unnatural amino acids that can be formed in food submitted to thermal treatment, especially in alkaline conditions. The paper presents an optimization of the synthetic procedure for the preparation of a standard of OAL that could be very useful to study the toxicological and nutritional consequences of the presence of OAL in food. In the meantime, it was possible to develop a method based on nuclear magnetic resonance for the diastereomeric characterization of LAL and OAL without derivatization. Interest in this method is based on the known differences in the nephrotoxicity of the two diastereisomers of LAL.

1H-, 13C-, 31P-NMR studies and conformational analysis of NADP+, NADPH coenzymes and of dimers from electrochemical reduction of NADP+

All H,H, H,P and several C,P coupling constants, including those between C-4' and the vicinal phosphorus atom, have been determined for NADP+, NADPH coenzymes and for a 4,4-dimer obtained from one-electron electrochemical reduction of NADP+. From these data the preferred conformation of the ribose, that of the 1,4-dihydronicotinamide rings, and the conformation about bonds C(4')-C(5') and C(5')-O(5') were deduced. The preferred form of the 1,4- and 1,6-dihydropyridine rings and the conformation about the ring-ring junction were also obtained for all the other 4,4- and 4,6-dimers formed in the same reduction. All the dimers show a puckered structure, i.e., a boat form for the 1,4- and a twist-boat for the 1,6-dihydronicotinamide ring; both protons at the ring-ring junctions are equatorial and have preferred gauche orientation. On the contrary, the reduced coenzyme NADPH displays a planar or highly flexible conformation, rapidly flipping between two limiting boat structures. The conformation of the ribose rings, already suggested for the NADP coenzymes to be an equilibrium mixture of C(2')-endo (S-type) and C(3')-endo (N-type) puckering modes, has been reexamined by using the Altona procedure and the relative proportion of the two modes has been obtained. The S and N families of conformers have almost equal population for the adenine-ribose, whereas for the nicotinamide-ribose rings the S-type reaches the 90%. The rotation about the ester bond C(5')-O(5') and about C(4')-C(5'), defined by torsion angles beta and gamma respectively, displays a constant high preference for the trans conformer beta t (75-80%), whereas the rotamers gamma are spread out in a range of different populations. The values are distributed between the gauche gamma + (48-69%) and the trans gamma t forms (28-73%). The gamma + conformer reaches a 90% value in the case of NADP+ and NMN+. The conformations of the mononucleotides 5'-AMP, NMN+ and NMNH were also calculated from the experimental coupling constant values of the literature.

1H-NMR study and structure determination of 4,4- and 4,6-dimers from electrochemical reduction of NADP+

The products arising from one-electron electrochemical reduction of the coenzyme nicotinamide adenine dinucleotide phosphate (NADP+) have been studied by HPLC chromatography and 1H-NMR spectroscopy. HPLC and NMR analyses have shown seven dimeric species, the most abundant of which (40%) has been isolated and has resulted to be an NADP 4,4-linked dimer. The other two diastereoisomeric 4,4-dimers present for the 25% and 10%, respectively, have been detected in the crude reaction mixture, but have not been isolated. The 4,4-tetrahydrobipyridine structure and the stereochemistry at the ring-ring junction for these three isomers have been determined on the basis of their NMR parameters. Preparative HPLC chromatography also led to two fractions enriched in another four dimers, present in the crude mixture, which turned out to have a 4,6-tetrahydrobipyridine structure. All the chemical shifts and the H,H coupling constants of the 4,4- and 4,6-tetrahydrobipyridine systems have been obtained for the seven compounds. For the most abundant among the 4,4-dimers the NMR analysis also gave the coupling constant values of the ribose-diphosphate chain.