Phomopsis sp. FT-0211, a soil isolate, was found to produce inhibitors of Hpid droplet formation in mouse peritoneal macrophages. Structurally related new compounds designated phenochalasins A and B were isolated from the fermentation broth of the producing strain by solvent extraction, ODS column chromatography and preparative HPLC. Phenochalasin A caused a dose-dependent reduction in the number and size of lipid droplets in macrophages without any cy to toxic effect at least up to 20 μM. On the other hand, phenochalasin B showed inhibition of lipid droplet formation with a severe cytotoxic effect on macrophages.
The structures of phenochalasins A and B were elucidated by spectroscopic studies including various NMR measurements. Phenochalasins A and B have the cytochalasan skeleton of the 21, 23-dioxa, 17, 22-dione moiety containing unique phenyl and O-methyl phenyl residues at the C-10 position, respectively.
A series of novel 6-substituted 5, 6-dihydro-5-hydroxy-α-pyrone esters, 1-3, isolated from fermentations of a Phomopsis sp. (Xenova culture collection no. X22502) have been identified as inhibitors of lipopolysaccharide (LPS)-induced cytokine production. These include the (6S)-4, 6-dimethyldodecadien-2E, 4E-dienoyl ester of phomalactone, 1, and two analogues bearing a prop-2E-enoic acid moiety at the 6-position of the α-pyrone ring. (6S)-4, 6-Dimethyl-2E, 4E-dienoic acid, 4, and a hydroxylated analogue, 5, were also isolated and characterised. The most potent cytokine production inhibitor was 1, which inhibited EPS-induced tumour necrosis factor α (TNFα) production by U937 cells and EPS-induced interleukin 1β (IL-1β) production by peripheral blood mononuclear cells (PBMC) with IC50 values of 80 nM and 190nM respectively. The effect of 1 in PBMC was selective for IL-1β relative to TNFα. The inhibition of IL-1β production by 1 involved a post-translational mechanism of action at the leyel of IL-1β secretion as demonstrated by the lack of an effect on cell-associated IE-1β production. 1 showed no effect on the activity of caspase 1 in cytosolic extracts from the THP1 monocytic cell line.
A new depsipeptide antibiotic, vinylamycin, was isolated from the culture broth of an actinomycete strain. The producing organism, designated MI982-63F1, was identified as a member of Streptomyces. Vinylamycin was isolated from the culture broth by extraction with EtOAc and purified by crystallization from EtOAc. The structure of vinylamycin was determined by spectroscopic analysis and degradation studies. Vinylamycin showed antimicrobial activities against Gram-positive bacteria including MRSA.
Antimalarial screening was performed for microbial metabolites that simulate artemisinin in their mode of action, a potent antimalarial component of an herbal remedy with a characteristic peroxide structure. Nanaomycin A was identified in this screen as an antimalarial compound, together with radicicol and several other compounds already reported (J. Antibiotics 51: 153-160, 1998). Nanaomycin A inhibited in vitro growth of the human malaria parasite Plasmodium falciparum with an IC80 value of 33.1 nM. It was as potent as radicicol and about 1/10 as potent as artemisinin. Studies on the mode of action suggested that the antimalarial action of the two non-peroxides, nanaomycin A and radicicol, involved heme-dependent radical generation, as is for the peroxide artemisinin. Namely, the inhibition of in vitro growth of malaria parasite by nanaomycin A or radicicol was reversed by tocopherol, a radical scavenger added to the assay mixture. Secondly, in a reaction system established for radical detection, in which a test radical donor and β-alanylhistidine as a radical recipient were incubated with and without hemin, the two compounds caused heme-dependent decreases of β-alanylhistidine, as did artemisinin. Among the 14 microbial metabolites identified during this screening, a correlation was observed between antimalarial activity and heme-dependent radical generating activity.
From a rare actinomycete strain #8 isolated from soil as arbekacin (ABK) resistant, we cloned a gene segment (0.9kb) conferring multiple resistance to aminoglycoside (AG) antibiotics with 6'-NH2 including semisynthetic ones except ABK and neomycin (NM). Enzymatic modification using cell free extracts from Streptomyces lividans TK21/pANT-S2 carrying the cloned gene revealed that the gene coded for an AG 6'-acetyltransferase [AAC(6')] capable of acetylating all of the tested AGs with 6'-NH2 including semisynthetic ones and astromicin. The substrate specificty of the enzyme was thus similar to that of AAC(6')-Ie of Enterococcus faecalis. Antibiotic assay revealed a weak but clear antibiotic activity of 6'-N-acetylABK (8% of ABK activity) in contrast with substantial inactivation by the AAC(6') of the other AGs including amikacin and isepamicin. The NM acetylation by the AAC(6') also did not result in NM inactivation. It seems thus likely that AAC(6')-dependent resistance to ABK and NM, if it emerges, will remain at low level.
A gene, blmB, encodes a bleomycin (Bm) N-acetyltransferase, designated BAT, from Bmproducing Streptomyces verticillus and confers resistance to Bm in Streptomyces and Escherichia coll. COS-1 cells transfected with a plasmid designated pEF-BOS/blmB, in which blmB is under the control of a strong promoter from the human polypeptide chain elongation factor 1α, transiently produced BAT. Immuno-cytochemical analysis using an anti-BAT monoclonal antibody revealed that BAT was localized in the nucleus of the blmB-carrying COS-1 cells. NIH/3T3 cells, transfected with pEF-BOS/6/blmB, stably expressed BAT at least for one month. The stable transformants of blmB showed specific resistance to the Bm family of antibiotics, suggesting that blmB has potential as a selective marker in gene transfer studies with mammalian cells.
The synthesis and biological properties of 1β-methylcarbapenems with 1-methyl-5-oxopyrrolidin-3-ylthio group at the C-2 position were studied. The sodium (1R, 5S, 6S)-6-[(R)-1-hydroxyethyl]-1-methyl-2-[(R)-1-methyl-5-oxopyrrolidin-3-ylthio]-1-carbapen-2-em-3-carboxylate and its (S)-isomer at the 2-position show potent and well-balanced antibacterial activity. The pharmacokinetic parameters of the pivaloyloxymethyl esters of these two carbapenems were compared in mice. The in vivo potency of these carbapenems was compared with that of cefdinir. Good in vivo efficacy of these ester prodrugs reflected the high and prolonged blood levels in parent drugs achieved after oral administration to mice.
The novel erythromycin A derivatives: 9(S)-9-dihydro-12-O-methylerythromycin A (6) and 12-O-methyerythromycin A (3), have been prepared using a new synthetic approach. The critical step is the regioselective methylation of the 12-hydroxyl of the boron complex of 2', 4''-0-bis(trimethylsilyl)-9(S)-9-dihydroerythromycin A (8), which has unprotected 6-, 9- and 11-hydroxyl groups. The antibacterial activities of these new derivatives were compared with those of erythromycin A (1), clarithromycin (2) and 9(S)-9-dihydroclarithromycin (5).