The Antimicrobial Activity of Annona emarginata (Schltdl.) H. Rainer and Most Active Isolated Compounds against Clinically Important Bacteria.

Annona emarginata (Schltdl.) H. Rainer, commonly known as "arachichú", "araticú", "aratigú", and "yerba mora", is a plant that grows in Argentina. Infusions and decoctions are used in folk medicine as a gargle against throat pain and for calming toothache; another way to use the plant for these purposes is chewing its leaves. Extracts from bark, flowers, leaves, and fruits from A. emarginata were subjected to antibacterial assays against a panel of Gram (+) and Gram (-) pathogenic bacteria according to Clinical and Laboratory Standards Institute protocols. Extracts from the stem bark and leaves showed moderate activity against the bacteria tested with values between 250⁻1000 µg/mL. Regarding flower extracts, less polar extracts (hexane, dichloromethane) showed very strong antibacterial activity against methicillin-sensitive Staphylococcus aureus ATCC 25923 and methicillin-resistant S. aureus ATCC 43300 with values between 16⁻125 µg/mL. Additionally, hexane extract showed activity against Klebsiella pneumoniae (MIC = 250 µg/mL). The global methanolic extract of the fruits (MeOHGEF) was also active against the three strains mentioned above, with MICs values 250⁻500 µg/mL. Bioassay-guided fractionation of MeOHGEF led to the isolation of a new main compound-(R)-2-(4-methylcyclohex-3-en-1-yl)propan-2-yl (E)-3-(4-hydroxyphenyl)acrylate (1). The structure and relative configurations have been determined by means of 1D and 2D NMR techniques, including COSY, HMQC, HMBC, and NOESY correlations. Compound 1 showed strong antimicrobial activity against all Gram (+) species tested (MICs = 3.12⁻6.25 µg/mL). In addition, the synthesis and antibacterial activity of some compounds structurally related to compound 1 (including four new compounds) are reported. A SAR study for these compounds was performed based on the results obtained by using molecular calculations.

A new series of antibacterial nitrosopyrimidines: synthesis and structure-activity relationship.

New nitrosopyrimidines were synthesized and evaluated as potential antibacterial agents. Different compounds structurally related with 4,6-bis(alkyl or arylamino)-5-nitrosopyrimidines were evaluated. Some of these nitrosopyrimidines displayed significant antibacterial activity against human pathogenic bacteria. Among them compounds 1c, 2a-c, and 9a-c exhibited remarkable activity against methicillin-sensitive and -resistant Staphylococcus aureus, Escherichia coli, Yersinia enterocolitica, and Salmonella enteritidis. A detailed structure-activity relationship study, supported by theoretical calculations, aided us to identify and understand the minimal structural requirements for the antibacterial action of the nitrosopyrimidines reported here. Thus, our results have led us to identify a topographical template that provides a guide for the design of new nitrosopyrimidines with antibacterial effects.

Penetratin and derivatives acting as antibacterial agents.

The synthesis, in vitro evaluation and conformational study of penetratin and structurally related derivatives acting as antibacterial agents are reported. Among the compounds evaluated here, two methionine sulphoxide derivatives (RQIKIWFQNRRM[O]KWKK-NH2 and RQIKIFFQNRRM[O]KFKK-NH2 ) exhibited the strongest antibacterial effect in this series. In order to better understand the antimicrobial activity obtained for these peptides, we performed an exhaustive conformational analysis using different approaches. Molecular dynamics simulations were performed using two different media (water and trifluoroethanol/water). The results of these theoretical calculations were corroborated using experimental CD measurements. The electronic study for these peptides was carried out using molecular electrostatic potentials obtained from RHF/6-31G(d) calculations. In addition, the non-apeptide RQIRRWWQR-NH2 showed strong inhibitory action against the Gram-negative and Gram-positive bacteria tested in this study.

Structure-activity relationship study of nitrosopyrimidines acting as antifungal agents.

The design, synthesis, in vitro evaluation, and conformational study of nitrosopyrimidine derivatives acting as antifungal agents are reported. Different compounds structurally related with 4,6-bis(alkyl or arylamino)-5-nitrosopyrimidines were evaluated. Some of these nitrosopyrimidines have displayed a significant antifungal activity against human pathogenic strains. In this paper, we report a new group of nitrosopyrimidines acting as antifungal agents. Among them, compounds 2a, 2b and 15, the latter obtained from a molecular modeling study, exhibited antifungal activity against Candida albicans, Candida tropicalis and Cryptococcus neoformans. We have performed a conformational and electronic analysis on these compounds by using quantum mechanics calculations in conjunction with Molecular Electrostatic Potentials (MEP) obtained from B3LYP/6-31G(d) calculations. Our experimental and theoretical results have led us to identify a topographical template which may provide a guide for the design of new nitrosopyrimidines with antifungal effects.

Synthesis and cytotoxic activity of 4-N-carboxybutyl-5-fluorocytosyl-Arg-Gln-Trp-Arg-Arg-Trp-Trp-Gln-Arg-NH2.

The chemical synthesis of 4-N-carboxybutyl-5-fluorocytosine (II) in solution phase starting from 5-fluorocytosine and the solid phase synthesis of Arg-Gln-Trp-Arg-Arg-Trp-Trp-Gln-Arg-NH(2) attached to the 4-N-carboxybutyl-5-fluorocytosine residue at the N-terminus of the peptide (III) via peptide bond formation is reported. The target compound exhibited a significant cytotoxic activity against a culture of HepG2 cells. In addition our results demonstrated that this new compound affect cell viability, produce mitochondrial dysfunction as well as interfere with intracellular calcium homeostasis control; leading to cell malfunction and death.

New antifungal peptides. Synthesis, bioassays and initial structure prediction by CD spectroscopy.

The synthesis, in vitro evaluation and conformational study of KKWKMRRNQFWIKIQR-NH(2), HFRWRQIKIWFQNRRMKWKK-NH(2) and RQPKIWFPNRRKPWKK-NH(2) acting as antifungal agents are reported. These peptides displayed a moderate but significant antifungal effect against both pathogenic fungi Candida albicans and Cryptococcus neoformans. The conformational analysis of these peptides was carried out using both theoretical and experimental methods.

Effects of dimethylformamide and L-menthol permeation enhancers on transdermal delivery of quercetin.

In this work a feasibility study of transdermal delivery system for quercertin (Q) in carbopol gel through abdominal hairless pig skin in vitro was performed. Dimethylformamide (DMF) and L-menthol (M) were selected as enhancers. Permeation experiences were carried out by using Franz-type diffusion cells. Phosphate saline buffer (pH 7.4) was used in the receptor compartments. All the system was maintained at 32 +/- 0.5 degrees C with a circulating water jacket and magnetic stirring (180 rpm). Samples were analysed by UV-VIS spectrophotometer at 255 nm. Flux (Jm) values, permeation (P) and diffusion (D) coefficients were obtained. Results of Q in CG permeation experiences with different percentages of DMF and M showed that 16.7% DMF and 1.95% L-menthol enhancers were the best quantities for the system tested. Enhancer effect can be attributed to direct action on membrane structure by promoting its distension. Therefore, enhancer substitutes for water in pores, improving active principal permeation through pig skin. M significantly increases Q permeation about 17 times higher than control. The results of permeation experiments with M and DMF using the same enhancer concentration (1.42%) conclude that M action is 9 times higher than DMF, approximately, indicating that M is an effective enhancer for a transdermal therapeutic system of Q in CG as vehicle.

Salicylic acid permeation: a comparative study with different vehicles and membranes.

Considering the skin's function, different dermal pharmaceutical forms can be developed according to the type of therapeutic activity, active principle and excipients involved in the formulation, such as "transdermal preparations". In the present study, the permeation parameters of the non-steroidal anti-inflammatory drug, salicylic acid (SA) through synthetic membrane, polyvinyliden difluoride, and a biological membrane, egg shell membrane, with different vehicles, propylene glycol, isopropyl alcohol and carbopol gel, were determined. The reported physicochemical parameters of SA from CG were significantly higher than those obtained using PG and IP. This is attributed to the lipophilic nature of the vehicle that facilitates the release and penetration of the active principle, thus acting sinergically. The permeation profiles of SA allow us to state that permeation kinetics is of first order, so that the flux values obtained are in direct proportion to the specific rates of drug release.

A comparative study of bacteriostatic activity of synthetic hydroxylated flavonoids

Among other properties, flavonoids present a notable bacteriostatic activity. In this paper, minimal inhibitory concentrations (MICs) of 5,7,4'-trihydroxyflavanone (naringenin), 5,7-dihydroxyflavone and 2',4',4- trihydroxychalcone (isoliquitirigenin) against Staphylococcus aureus ATCC 25 923 were determined and compared to values obtained for other chalcones and flavanones previously investigated. Specific growth rates and MICs were determined by a turbidimetric kinetic method. The observed sequence MICflavanone (inactive) >MIC7-hidroxyflavanone (197.6 µgml-1)>MIC5,7,4'-trihydroxyflavanone (120 µgml-1) showed that the introduction of an electron donating group (-OH) causes an increase in bioactivity. On the other hand, the comparisons MIC5,7,4'-trihydroxyflavanone (120 µgml-1) >>> MIC2',4',4-trihydroxychalcone (29 µgml-1) and MIC5,7-dihydroxyflavone (105 µgml-1) >>> MIC2',4'-dihydroxychalcone (28.8 µgml-1) indicated that the chalcone structure is the most favourable for bacteriostatic activity within the flavonoid family.