Influence of soil texture on hydraulic properties and water relations of a dominant warm-desert phreatophyte.

We investigated hydraulic constraints on water uptake by velvet mesquite (Prosopis velutina Woot.) at a site with sandy-loam soil and at a site with loamy-clay soil in southeastern Arizona, USA. We predicted that trees on sandy-loam soil have less negative xylem and soil water potentials during drought and a lower resistance to xylem cavitation, and reach E(crit) (the maximum steady-state transpiration rate without hydraulic failure) at higher soil water potentials than trees on loamy-clay soil. However, minimum predawn leaf xylem water potentials measured during the height of summer drought were significantly lower at the sandy-loam site (-3.5 +/- 0.1 MPa; all errors are 95% confidence limits) than at the loamy-clay site (-2.9 +/- 0.1 MPa). Minimum midday xylem water potentials also were lower at the sandy-loam site (-4.5 +/- 0.1 MPa) than at the loamy-clay site (-4.0 +/- 0.1 MPa). Despite the differences in leaf water potentials, there were no significant differences in either root or stem xylem embolism, mean cavitation pressure or Psi(95) (xylem water potential causing 95% cavitation) between trees at the two sites. A soil-plant hydraulic model parameterized with the field data predicted that E(crit) approaches zero at a substantially higher bulk soil water potential (Psi(s)) on sandy-loam soil than on loamy-clay soil, because of limiting rhizosphere conductance. The model predicted that transpiration at the sandy-loam site is limited by E(crit) and is tightly coupled to Psi(s) over much of the growing season, suggesting that seasonal transpiration fluxes at the sandy-loam site are strongly linked to intra-annual precipitation pulses. Conversely, the model predicted that trees on loamy-clay soil operate below E(crit) throughout the growing season, suggesting that fluxes on fine-textured soils are closely coupled to inter-annual changes in precipitation. Information on the combined importance of xylem and rhizosphere constraints to leaf water supply across soil texture gradients provides insight into processes controlling plant water balance and larger scale hydrologic processes.

6-Aminoquinolones: photostability, cellular distribution and phototoxicity.

Three selected aminoquinolones endowed with a potent antibacterial (compounds 1 and 2) and antiviral activity (compound 3) have been evaluated for their phototoxic properties in vitro. Photostability studies of these compounds indicate that compound 3 is photostable whereas compound 1 and in particular, compound 2 are rapidly photodegraded upon UVA irradiation, yielding a toxic photoproduct. Intracellular localization of these compounds has been evaluated by means of fluorescence microscopy using tetramethylrhodamine methyl ester and acridine orange, which are specific fluorescent probes for mitochondria and lysosomes, respectively. No co-staining was observed with lysosomal stain for all the test compounds. On the contrary compound 3 was found to be specifically incorporated in mitochondria. The compounds exhibited remarkable phototoxicity in two cell culture lines: human promyelocytic leukaemia (HL-60) and human fibrosarcoma (HT-1080). The quinolone-induced photodamage was also evaluated measuring the photosensitizing cross-linking in erythrocyte ghost membranes, the strand breaks activity and oxidative damage on plasmid DNA. The results show that these derivatives are able to photoinduce crosslink of erythrocytes spectrin, whereas do not significantly photocleavage DNA directly, but single strand breaks were observed after treatment of photosensitized DNA with two base excision repair enzymes, Fpg and Endo III respectively.

In vitro phototoxic properties of new 6-desfluoro and 6-fluoro-8-methylquinolones.

A representative set of potent antibacterial 6-desfluoro-8-methylquinolones, in which the C-6 fluorine atom is replaced by -NH(2) or -H, and their 6-fluoro counterparts, were investigated to evaluate their phototoxic potential and to explore the mechanism behind their phototoxicity. The capacity to photosensitize biological substrates (lipids, proteins, DNA) has been analyzed, as well as their photocytotoxicity on red blood cells and 3T3 murine fibroblasts. The results obtained show that the quinolones studied are able to photosensitize red blood cell lysis in an oxygen-dependent way and induce a high decrease in cell viability after UVA irradiation. A major correlation with phototoxicity lies in the structure of the individual antibacterials and their hydrophobicity; in particular, 6-amino derivatives are less phototoxic than corresponding unsubstituted and fluorinated compounds. Cellular phototoxicity was inhibited by the addition of free radical and hydroxyl radical scavengers (BHA, GSH and DMTU), suggesting the involvement of a radical mechanism in their cytotoxicity. A good correlation was observed between lipid peroxidation and phototoxicity, indicating that the test compounds exert their toxic effects mainly in the cellular membrane. Preliminary experiments on pBR322 DNA show that these derivatives do not photocleave DNA, differently from the two photogenotoxic fluoroquinolones, ciprofloxacin and lomefloxacin, used as reference compounds.

Carbon isotope discrimination and bundle sheath leakiness in three C(4) subtypes grown under variable nitrogen, water and atmospheric CO(2) supply.

The changes in composition and productivity of semi-arid C(4) grassland, anticipated with rising atmospheric CO(2), will depend on soil water and nutrient availability. The interactive effects of soil resource limitation and elevated CO(2 )on these grasses, furthermore, may vary among C(4) biochemical subtypes (NADP-ME, NAD-ME, PCK) that differ in bundle sheath leakiness (Phi) responses to drought and nitrogen supply. To address C(4) subtype responses to soil resource gradients, the carbon isotope discrimination (Delta), bundle sheath leakiness (Phi), leaf gas exchange (A, g(s), c(i)/c(a)) and above-ground biomass accumulation were measured on three dominant grasses of semi-desert grassland in south-eastern Arizona. Bouteloua curtipendula (PCK), Aristida glabrata (NADP-ME) and the non-native Eragrostis lehmanniana (NAD-ME) were grown in controlled-environment chambers from seed under a complete, multi-factorial combination of present ambient (370 ppm) and elevated (690 ppm) CO(2) concentration and under high and low water and nitrogen supply. E. lehmanniana (NAD-ME) had the highest photosynthetic rate (A) and lowest Phi compared to the other two grasses when grown under low nitrogen and water availability. However, favourable water and nitrogen supply and elevated atmospheric CO(2) enhanced photosynthetic performance and above-ground biomass production of B. curtipendula (PCK) to a greater extent than in A. glabrata and E. lehmanniana. Contrary to pre vious studies, Phi and Delta in the NADP-ME subtype (A. glabrata) were most affected by changing environmental conditions compared to the other subtypes; deviations from the classic NADP-ME anatomy in Aristida could have accounted for this result. Overall, response of semi-arid grasslands to rising atmospheric CO(2) may depend more on species-specific responses to drought and nitrogen limitation than on general C(4) subtype responses.

Velnacrine thiaanalogues as potential agents for treating Alzheimer's disease.

The only therapeutic drugs for combating dementia disease are acetylcholine esterase inhibitors (AChEI). However, the use of tacrine, the first AChEI to be launched as an Alzheimer's disease (AD) drug, has been limited by serious side effects. Therefore, efforts to search for more potent and selective inhibitors of AChE still remain highly significant in the therapeutic treatment of AD. In this work we modified the cyclohexyl ring of velnacrine, a less toxic analogue of tacrine, by synthesizing a series of thiopyranoquinolines in which the C-3 methylene unit was replaced by a sulphur atom. The anti-AChE data show that the activity was maintained with the bioisosteric substitution carried out. The introduction of a chlorine atom at different positions of the aromatic ring resulted in an array of different activities. In an attempt to understand the different behaviours displayed by the chlorine-substituted derivatives, a molecular docking study was performed.

QSAR study and VolSurf characterization of anti-HIV quinolone library.

Antiviral quinolones are promising compounds in the search for new therapeutically effective agents for the treatment of AIDS. To rationalize the SAR for this new interesting class of anti-HIV derivatives, we performed a 3D-QSAR study on a library of 101 6-fluoro and 6-desfluoroquinolones, taken either from the literature or synthesized by us. The chemometric procedure involved a fully semiempirical minimization of the molecular structures by the AMSOL program, which takes into account the solvatation effect, and their 3D characterization by the VolSurf/GRID program. The QSAR analysis, based on PCA and PLS methods, shows the key structural features responsible for the antiviral activity.

6-hydroxy derivative as new desfluoroquinolone (DFQ): synthesis and DNA-binding study.

A new 6-desfluoroquinolone derivative, characterized by the presence of a 6-hydroxyl group instead of the usual fluorine atom at the C-6 position, was synthesized with the aim to better understand the mechanistic role of the C-6 substituent in the quinolone/DNA/DNA-gyrase interaction. The antibacterial activity unambiguously shows that the hydroxyl group is a good substitute for the C-6 fluorine atom, especially against Gram-positive bacteria. On the contrary, it is a very weak inhibitor of the target DNA gyrase, displaying the highest IC50 value observed for all the C-6 substituted analogues. This behaviour could be explained on the basis of its DNA binding properties.

6-Aminoquinolones as new potential anti-HIV agents.

A series of 6-aminoquinolone compounds were evaluated for their in vitro activity against human immunodeficiency virus type 1 (HIV-1). Compound 12a, bearing a methyl substituent at the N-1 position and a 4-(2-pyridyl)-1-piperazine moiety at the C-7 position, was the most active in inhibiting HIV-1 replication on de novo infected C8166 human lymphoblastoid cell lines. The 12a EC(50) value was 0.1 microM, a 7-20-fold lower concentration relative to that for compounds 8a and 7a containing a cyclopropyl and tert-butyl substituent at the N-1 position, respectively. When the C-6 amino group was replaced with a fluorine atom, a decreased antiviral effect was observed. The observed effects are selective, since potency is substantially reduced when testing the compounds against the herpes simplex virus type 1 (HSV-1). Active quinolone derivatives very efficiently interact with TAR RNA, which suggests a nucleic acid-targeted mechanism of action.

Chemometric rationalization of the structural and physicochemical basis for selective cyclooxygenase-2 inhibition: toward more specific ligands.

The discovery that proinflammatory prostaglandins are produced by cyclooxygenase-2 (COX-2), an inducible isoform of the constitutive cyclooxygenase-1 (COX-1), opened a new frontier in the treatment of inflammatory diseases, because the selective inhibition of COX-2 can lead to therapeutically effective compounds which do not have the common side effects of classical non-steroidal antiinflammatory drugs (NSAIDs). Different crystallographic structures of both free COX-1 and COX-2 as well as complexes with inhibitors have been solved. Because of the great similarity between the two enzymes, it is difficult to detect the most important structural and physicochemical features that would be useful for designing inhibitors with an improved selectivity. In this paper we describe the application of a chemometric procedure to the study of COX-2 selective inhibition. This method, developed to reveal the most suitable regions of isoenzymes for the design of selective ligands, also has a very practical utility. GRID multivariate characterization of the enzymes and subsequent Principal Component Analysis (PCA) of the descriptor variables allow the identification of chemical groups that could be added to a core template structure to increase ligand selectivity.

(1,4-Benzothiazinyloxy)alkylpiperazine derivatives as potential antihypertensive agents.

A series of compounds having a piperazine moiety variously linked to the benzothiazine nucleus were synthesized and evaluated for their in vitro alpha-adrenoceptor affinity by radioligand receptor binding assays. Some compounds bearing a oxyalkyl-(2-methoxyphenyl)piperazine side chain were good alpha1-adrenoreceptor ligands.

Design and synthesis of modified quinolones as antitumoral acridones.

The bacterial topoisomerase II (DNA gyrase) and the mammalian topoisomerase II represent the cellular targets for quinolone antibacterials and a wide variety of anticancer drugs, respectively. In view of the mechanistic similarities and sequence homologies exhibited by the two enzymes, tentative efforts to selectively shift from an antibacterial to an antitumoral activity was made by synthesizing a series of modified tricyclic quinolones, in which the essential 3-carboxylic function is surrogated by phenolic OH and the classic C-6 fluorine atom is replaced by a NH2 group. The resulting 7-amino-9-acridone derivatives were assayed for their antibacterial as well as cytotoxic activities. No antibacterial activity was found. On the other hand, many derivatives showed significant cytotoxic activity against both HL-60 and P388 leukemias and a wide panel of human and rodent solid tumor cells, derivatives 25 and 26 displaying the best overall antiproliferative activity. Against the LoVo cell line, derivative 25 exhibited higher cytotoxic effects than etoposide.

Studies on 6-aminoquinolones: synthesis and antibacterial evaluation of 6-amino-8-ethyl- and 6-amino-8-methoxyquinolones.

From our quantitative structure-activity relationship (QSAR) study on a large set of 6-aminoquinolones, which indicated that a group larger than methyl could be allocated at C-8 position, we have synthesized two new series of 6-aminoquinolones characterized by the presence of an ethyl or a methoxy group at C-8 position. The antibacterial evaluation shows that, while the 8-ethyl derivatives were devoid of any antibacterial activity, the introduction of methoxy group gave compounds with good antibacterial activity, especially against gram-positive bacteria. A tentative explanation of the different behaviours among the 8-substituted analogues is given taking into account both the length and electronic properties of the C-8 groups.

Mg(2+)-mediated binding of 6-substituted quinolones to DNA: relevance to biological activity.

The interaction of a number of novel 6-substituted quinolone derivatives with DNA in the presence/absence of magnesium ions has been investigated by fluorometric techniques. The drug-single-stranded nucleic acid interaction is invariantly mediated by the metal ion. In all cases optimal complex formation is found at physiological Mg2+ concentration. From titrations at different [Mg2+] the binding constant for the ternary drug-DNA-Mg2+ complex (KT) has been evaluated. Interestingly, a good relationship is found between KT and gyrase poisoning activity of the test quinolones (IC50), which confirms that DNA-affinity of the quinolone, modulated by Mg2+, plays an important role in poisoning the cleavable gyrase-DNA complex and, consequently, in eliciting antibacterial activity in this family of drugs. The results obtained with different 6-substituted compounds supports the idea that position 6 of the drug, besides playing a pharmacokinetic role, is involved in recognition of the enzyme pocket. Our data do not support a mechanism of action based upon quinolone intercalation into B-DNA.

Synthesis and antibacterial evaluation of [1,3]benzothiazino[3,2-a]quinoline- and [3,1]benzothiazino[1,2-a]quinoline-6-carboxylic acid derivatives.

A series of [1,3]benzothiazino[3,2-a]quinoline- (5) and [3,1]benzothiazino[1,2-a]quinoline-6-carboxylic acids (10) were synthesized and evaluated for their in vitro antibacterial activity. The activity is discussed in terms of their structural features revealed by molecular orbital correlation.

Chemometric methodologies in a quantitative structure-activity relationship study: the antibacterial activity of 6-aminoquinolones.

The paper illustrates the chemometric strategies appropriate for extracting information from a large amount of biological data regarding the antibiotic activity of 6-aminoquinolones. The unique framework based on principal component analysis, projection onto latent structures, and response surface methodologies permits the structure-activity correlations to be shown and to suggest new compounds for further testing. The low activity of the suggested molecules points out the limitations of quantitative structure-activity relationship models when the training set is not properly designed in order to balance all the structural variations taken into account.

Potent 6-desfluoro-8-methylquinolones as new lead compounds in antibacterial chemotherapy.

In a furtherance of our SAR study on the C-6 position of quinolone antibacterials, a series of 6-desfluoro-8-methylquinolones were synthesized and evaluated for their in vitro antimicrobial activity. As a result of this study, compounds with strong activity against Gram-positive bacteria, including ciprofloxacin-resistant and methicillin-resistant Staphylococcus aureus, were identified. The best Gram-positive antibacterial activity was exhibited by piperidinyl derivative 6c, which was 17 times more potent than ciprofloxacin and displayed extremely high activity against Streptococcus pneumoniae with an MIC value of <0.016 microg/mL. Thus, we have shown that substituent combinations in the quinolone ring, excluding the C-6 fluorine atom, might produce powerful antibacterial agents.

Studies on 6-aminoquinolones: synthesis and antibacterial evaluation of 6-amino-8-methylquinolones.

The 6-aminoquinolone had previously been identified as a new class of quinolone antibacterial agents. To continue our structure-activity relationship (SAR) study in this series, novel 6-amino-8-methylquinolone derivatives have now been synthesized and evaluated for in vitro antibacterial activity. We have shown that the coupled presence of a methyl group at the C-8 position with an amino group at C-6 is effective for enhancing antibacterial activity, particularly against Gram-positive bacteria. The SARs associated with the N-1, C-6, and C-7 are discussed. The 1,2,3,4-tetrahydroisoquinolinyl derivative 19v showed the highest antibacterial activity with MIC values on Gram-positive bacteria superior to that of ciprofloxacin, especially against Staphylococcus aureus strains, including those strains which are methicillin-and ciprofloxacin-resistant.

6-Aminoquinolones: a new class of quinolone antibacterials?

A series of quinolone- and 1,8-naphthyridone-3-carboxylic acids, designed by previous QSAR studies and characterized by an amino group at the C-6 position instead of the usual fluorine atom, were synthesized for the first time and evaluated for in vitro antibacterial activity. All of the synthesized compounds maintain good activity against Gram-negative bacteria (Pseudomonas aeruginosa excluded), and those compounds having a thiomorpholine group as the C-7 substituent also have good activity against Gram-positive bacteria. Some aspects of structure-activity relationships associated with the C-1, C-5, C-7, and C-8 substituents are also discussed. Derivatives 18g and 38g displayed the best activity with geometric mean MICs of 0.45 and 0.66-0.76 micrograms/mL against Gram-negative and Gram-positive bacteria, respectively. This antimicrobial activity reflects their ability to inhibit bacterial DNA-gyrase. The results of this study show that, while the C-6 fluorine is still the preferred substituent, good activity can still be obtained by replacing it with an amino group.

7-(Disubstituted thiazolyl)-3,5-dihydroxy-6-heptenoic/heptanoic acid derivatives as HMG-CoA reductase inhibitors.

A series of disubstituted thiazoles, functionalized with the essential 3,5-dihydroxy-6-heptenoic or heptanoic chain, were prepared and evaluated for their ability to inhibit the enzyme HMG-CoA reductase in vitro. All the synthesized compounds 46-61 showed a moderate inhibitory potency.