Cyclic voltammetric, fluorescence and biological analysis of purified aeruginosin A, a secreted red pigment of Pseudomonas aeruginosa PAO1.

The opportunistic pathogen Pseudomomas aeruginosa produces multiple pigments during in vitro culture and in vivo during colonization of burn wounds and in the airways of cystic fibrosis (CF) patients. One pigment is a deep 'merlot'-coloured compound known as aeruginosin A (AA). However, the red pigment(s) of P. aeruginosa are often collectively called pyorubrin, of which there is no known chemical composition. Here, we purified and confirmed by MS and assessed the physicochemical properties of AA (2-amino-6-carboxy-10-methylphenazinium betaine) by first focusing on its ability to redox-cycle using cyclic voltammetry and its spectroscopic (as well as fluorescent) properties, experiments that were conducted at physiological pH. AA exhibited reversible electrochemistry at a glassy carbon electrode within a potential range of -500 to -200 mV. Electrochemical anodic and cathodic peak currents were observed at -327 and -360 mV, respectively, with a low formal reduction potential of -343.5 mV versus Ag/AgCl. AA absorbed at 516 nm and fluoresced at 606 nm. Results from the spectro-electrochemistry of pyorubrin revealed that its strongest fluorescence was in its parent or oxidized form. Production of AA by P. aeruginosa was found to be controlled by the rhl component of the intercellular signalling system known as quorum sensing and was produced maximally during the stationary growth phase. However, unlike its downstream blue redox-active toxin, pyocyanin, AA had no adverse effects on methicillin-resistant Staphylococcus aureus USA300, Escherichia coli DH5-α or human keratinocytes. We close with some thoughts on the potential commercial use(s) of AA.

Cleavage of the cyclohexyl-subunit of rapamycin results in loss of immunosuppressive activity.

The cyclohexyl-subunit of rapamycin was cleaved by a sequence involving a Baeyer-Villiger reaction and acid hydrolysis of the resulting lactone-acetal as key steps. Binding of this new rapamycin derivative to FKBP12 was only slightly reduced by this modification, whereas the loss of antiproliferative and immunosuppressive activity was dramatic. These findings indicate that part of the cyclohexyl-subunit of rapamycin could belong to its effector domain.

Preparation and in vitro activities of ethers of [D-serine]8-cyclosporin.

Reactions of the [D-serine]8-cyclosporin (2) with a series of alkylating agents under phase transfer conditions gave the alkylated products 3-6. Alkylations of 2 with hindered esters of bromoacetate gave the crystalline esters 7 and 8. Hydrolysis under basic conditions gave the acid 10. Reduction of ester 8 led to a novel cyclosporin 11. This was transformed in two additional steps to 15. In a similar two-step sequence 17 was prepared from 15. From 2 and methyl 2-(bromomethyl)acrylate product 20 was obtained. Alkylation of 2 with 49 followed by deprotection yielded 24. The linear isomer 27 was prepared. The 3-hydroxypropyl ether 30 was prepared in two steps from 28. The 4-hydroxybutyl ether 31 was accessible from 2 and 1,4-dibromobutane. The hydroxy group of 11 was converted to the tosylate 32. Base treatment of 32 led to the bicyclic [3(R)-morpholinecarboxylic acid]8-cyclosporin (39). The [2-ethoxy-5-morpholinecarboxylic acid]8-cyclosporin 40 was prepared via 36. Base treatment of the bromoacetate 37 gave the morpholinone derivative 41. [4(R)-Oxazolidinecarboxylic acid]8-cyclosporin (42) was obtained from 2 and methylene bromide. From 24 the tosylate 38 was prepared and cyclized to the hexahydrooxazepine derivative 43. [2(R)- Piperidinecarboxylic acid]8-cyclosporin (49) was prepared from 42 and 2(R)-piperidinecarboxylic acid 45 via 46-48. The bicyclic cyclosporin 39 was found to be about 3-4 times more active than cyclosporin A in our in vitro tests.

[Enterobacteriaceae isolated in nine general hospitals of the Ile-de-France in 1988 and 1989: susceptibility to beta-lactam antibiotics according to the length of hospitalisation]. / Sensibilité aux bêtalactamines en fonction de la durée d'hospitalisation des entérobactéries isolées dans neuf hôpitaux généraux d'Ile-de-France en 1988 et 1989.

Susceptibility to beta-lactam antibiotics of strains of Enterobacteriaceae consecutively isolated in nine general hospitals during a period of 2 months (march and april) has been studied by the disk-agar diffusion method. The separation between susceptible and resistant strains was based on the measure of the inhibition zones centered by 2 disks: cephalothin and ticarcillin. Enterobacteriaceae were divided in 2 groups: strains isolated during the first 48 h of hospitalisation or isolated after. Fifty one per cent of the strains were isolated during the first 48 h: they did not belong to the residential flora of these hospitals. Klebsiella, Proteus indole positive, Providencia, Enterobacter, Serratia were more frequently isolated after 48 h of hospitalisation. Susceptible strains of Klebsiella, Proteus indole positive, Providencia, Serratia were more rarely isolated after 48 h of hospitalisation. E. coli whatever the duration of hospitalisation, is the less frequent susceptible bacterium.