New anthracycline antibiotics 3′-O-demethyl mutactimycin (3) and 4-O, 3′-O-didemethyl mutactimycin (4) were isolated from two actinomycetes strains, Nocardia transvalensis and Streptomyces sp. GW 60/1571. The chemical structures were elucidated by mass spectrometry and NMR spectroscopy. Antibiotic 3 displayed moderate antimicrobial activity against Gram-positive bacteria and cytotoxicity against P388, L1210 and HeLa tumor cells (IC50; 9.6, > 25 and 20 μg/ml, respectively).
A new secondary metabolite was detected in the culture filtrate and extracts of Streptomyces violaceusniger Tü 4113 by HPLC-diode-array and HPLC-electrospray-mass-spectrometry screening. The compound named spirofungin has a polyketide-spiroketal structure and shows various antifungal activities, particularly against yeasts.
Two new antibiotics, hongoquercins A and B, were isolated from fermentation extracts of the unidentified fungus LL-23G227. In the optimum medium, titers of the A and B components reached approximately 2.1 g/liter and 0.02 g/liter, respectively. The optimum temperature for antibiotic production was approximately 22°C. Growth was delayed at 15°C but appeared to reach higher levels than was observed at 22°C. Addition of dextrose to growth media increased hongoquercin B production. Hongoquercin A exhibited moderate activity against Gram-positive bacteria. Mechanistic studies conducted in an E. coli imp strain suggested membrane damage as the primary mode of bactericidal action. These compounds also lysed human red blood cells, suggesting a similar mode of action on eukaryotic cells.
Strain MJ347-81F4 has been found to produce two new cyclic thiazolyl peptide antibiotics, components A and B. Taxonomic studies including morphological and physiological characteristics and chemical analysis of whole cells of the producing strain revealed this microorganism to belong to genus Amycolatopsis, and so we designated the strain Amycolatopsis sp. MJ347-81F4. After 10 to 12 days of fermentation, most of the antibacterial activity was present mainly in the mycelial cake and reached its maximum level. In comparison with reference compounds, A as the major component showed excellent in vitro activity against Gram-positive bacteria including highly methicillin-resistant Staphylococcus aureus (MRSA) and Enterococcus faecalis with MICs in the range of concentration of 0.006∼0.1 μg/ml. The results on the antimicrobial activity against thiazolyl peptide-resistant mutants of Bacillus subtilis NRRL B-558 indicated that the possible molecular target of MJ347-81F4 component A might be the 50S subunits of the ribosome, the inactivation of which would inhibit protein synthesis.
A systematic approach toward building activity against methicillin-resistant staphylococci into the cephalosporin class of β-lactam antibiotics is described. Initial work focused on finding the optimal linkage between the cephem nucleus and a biphenyl pharmacophore, which established that a thio linkage afforded potent activity in vitro. Efforts to optimize this activity by altering substitution on the pharmacophore afforded iodophenylthio analog MC-02, 002, which although highly potent against MRSA, was also highly bound to serum proteins. Further work to decrease serum protein binding showed that replacement of the iodo substituent by the positively-charged isothiouronium group afforded potent activity and reduced serum binding, but insufficient aqueous solubility. Solubility was enhanced by incorporation of a second positively-charged group into the 7-acyl substituent. Such derivatives (MC-02, 171 and MC-02, 306) lacked sufficient stability to staphylococcal β-lactamase enzymes. The second positive charge was incorporated into the cephem 3-substituent in order to utilize the β-lactamase-stable aminothiazolyl-(oximino)acetyl class of 7-substituents. These efforts culminated with the discovery of bis(isothiouroniummethyl)phenylthio analog MC-02, 331, whose profile is acceptable with respect to potency against MRSA, serum binding, aqueous solubility, and β-lactamase stability.
Kanamycin group antibiotics were subjected to enzymatic acetylation by a cell free extract containing an aminoglycoside 3-N-acetyltransferase, AAC(3)-X, derived from Streptomyces griseus SS-1198PR. Characterization of the incubated reaction mixtures by TLC and antibiotic assay revealed that a product retaining activity was specifically formed from arbekacin, an anti-MRSA semisynthetic aminoglycoside. The structural determination demonstrated that acetylation occurred at the 3″-amino group in arbekacin and amikacin, and at the 3-amino group in dibekacin as in the case of kanamycin. These results should reflected the effect of the (S)-4-amino-2-hydroxybutyryl side chain which is present in arbekacin and amikacin, but absent in dibekacin and kanamycin. The 3″-N-acetylation is the first finding in the enzymatic modifications of aminoglycoside antibiotics. 3″-N-Acetylarbekacin showed antibiotic activity as high as that of 2′-N-acetylarbekacin reported previously, whereas 3″-N-acetylamikacin showed no substantial activity. Thus, our results illuminated a novel aspect of arbekacin distinct from the other aminoglycosides.
Syringomycin E (SR-E), a new antifungal produced by the bacterium Pseudomonas syringae pv. syringae, was evaluated in a murine vaginal candidiasis model. In one study, mice were treated intravaginally b.i.d. for 4 days with drug carrier, SR-E 2% in either PEG-400 or PEG-ointment, or 1% clotrimazole as a positive control. Quantitative vaginal cultures were taken prior to treatment on day 1 and on days 5, 6, and 7. Both formulations showed a reduction of yeast colonization in the vaginas on day 5 (P ≤0.06 and P ≤0.03 for SR-E/PEG-400 and SR-E/PEG ointment, respectively) and SR-E/PEG ointment reduced the colonization on day 7 (P ≤0.06) when compared to carrier treated controls. In a second study, SR-E was formulated in Aquaphor at three higher concentrations of SR-E [3%, 6%, or 12% (w/v)]. SR-E showed dose-dependent efficacy. The 3% dose showed no effect while the 6% and 12% doses reduced the number of yeasts. The 12% dose showed a significant reduction on days 5 (P ≤0.01), 6 (P ≤0.06), and 7 (P ≤0.03) when compared with the drug carrier controls and on day 5 was more effective than clotrimazole (P ≤0.03). Clotrimazole did not significantly reduce the yeasts in the vagina until days 6 (P ≤0.01) and 7 (P ≤0.01) when compared to the drug carrier controls. No vaginal inflammatory response was evident by histological examination in uninfected animals treated with SR-E. No SR-E could be detected in plasma, kidney, or liver. SR-E (12%) was an effective treatment when compared to 1% clotrimazole.
N-Demethylvancomycin, which has been clinically used in China, is one member of vancomycin group (glycopeptide) antibiotics. It differs from vancomycin only in that methyl group on the amino group of the N-terminal residue of vancomycin has been replaced by H. By reductive alkylation of N-demethylvancomycin, we synthesized N-alkyl and N, N′-dialkyl N-demethylvancomycins, which closely correlated with vancomycin in structure. The association constants of the complexes of N-demethylvancomycin and its analogues with di-N-Ac-L-Lys-D-Ala-D-Ala and the antibiotic activity against Staphylo-coccus aureus of the glycopeptides were determined. Results showed that N-demethylvancomycin has higher affinity for bacterial cell wall analogue di-N-Ac-L-Lys-D-Ala-D-Ala and more potent antibiotic activity against Staphylococcus aureus than vancomycin. Both N-alkylation and N, N′-dialkylation of N-demethylvancomycin reduced the affinity and antibiotic activity. The longer the alkyl groups, the less potent antibiotic activities and lower affinities have the glycopeptides. The antibiotic activities against Staphylococcus aureus of N-demethylvancomycin and its analogues roughly parallel their affinities for di-N-Ac-L-Lys-D-Ala-D-Ala.
The synthesis and antibacterial activity of 1β-methylcarbapenems with quaternary ammonium groups at the C-2 position have been studied. Two types of new carbapenem derivatives have been synthesized. These 1β-methylcarbapenems, one type having a (2S, 4S)-2-[1, 1-dimethyl-2-(1-piperazinyl)carbonyl]pyrrolidinio-4-ylthio group and the other type having a (2S, 4S)-2-(4-carbamoylmethyl-4-methylhomopiperazinio-1-ylcarbonyl)pyrrolidin-4-ylthio group, show potent and well balanced antibacterial activity as well as high stability against dehydropeptidase-I. The in vivo potency of these two carbapenems was compared with that of meropenem. The structure-activity relationships leading to these carbapenems are also described.
Five novel 3-hydroxyl derivatives of sixteen-membered macrolide possessing 4-O-acyl-α-L-cladinose as a neutral sugar moiety were synthesized by using a combination of structurally stable silyl acetal protection and selective hydrogenolysis of a 3″-methylthiomethyl ether to a 3″-OMe group. Several derivatives having n-butyryl, i-butyryl and n-valeryl substituent at the 4″-OH group exhibited significant antibacterial activity in vitro. One of them, 4″-O-n-butyryl-3″-O-methylleucomycin V, showed improved therapeutic effect in mice.
The first synthesis of siderophore conjugates of two macrolide antibiotics, spiramycin 1 and neospiramycin 2, which are unable to penetrate the outer membrane of Gramnegative bacteria are described. These novel conjugates were prepared by regioselective acylation of a hydroxyl function of 1 and 2 with a dihydroxybenzoic Fe(III) complexing ligand linked via a carboxyl group containing spacer to the macrolide antibiotics. The preliminary biological evaluation of these novel conjugates under standard and iron depleted conditions has shown that their antibacterial activity was comparable to that of spiramycin 1 and neospiramycin 2.
Forosamine at the 17-position of spinosyns A and D was hydrolyzed under mild acidic conditions to give the corresponding 17-pseudoaglycones. The tri-O-methylrhamnose at the 9-position of the 17-pseudoaglycone of spinosyn A was hydrolyzed under more vigorous acidic conditions to give the aglycone of spinosyn A. However, these conditions led to decomposition of the 17-pseudoaglycone of spinosyn D, presumably due to more facile protonation of the 5, 6-double bond to produce a tertiary carbonium ion which undergoes further rearrangements. Spinosyns J and L (3′-O-demethyl spinosyn A and D, respectively) obtained from fermentation of biosynthetically-blocked mutant strains of Saccharopolyspora spinosa, were oxidized to give the corresponding 3′-keto-derivatives and the resultant keto-sugars were then β-eliminated under basic conditions to give the 9-pseudoaglycones of spinosyns A and D respectively. Forosamine at the 17-position of the 9-pseudoaglycone of spinosyn D was then readily hydrolyzed to yield the aglycone of spinosyn D.