A new broad-spectrum aminoglycoside antibiotic complex, sporaricin. I. Fermentation, isolation and characterization

Heptose-containing bacterial natural products: structures, bioactivities, and biosyntheses

Covering: up to 2020Glycosylated natural products hold great potential as drugs for the treatment of human and animal diseases. Heptoses, known as seven-carbon-chain-containing sugars, are a group of saccharides that are rarely observed in natural products. Based on the structures of the heptoses, the heptose-containing natural products can be divided into four groups, characterized by heptofuranose, highly-reduced heptopyranose, d-heptopyranose, and l-heptopyranose. Many of them possess remarkable biological properties, including antibacterial, antifungal, antitumor, and pain relief activities, thereby attracting great interest in biosynthesis and chemical synthesis studies to understand their construction mechanisms and structure-activity relationships. In this review, we summarize the structural properties, biological activities, and recent progress in the biosynthesis of bacterial natural products featuring seven-carbon-chain-containing sugars. The biosynthetic origins of the heptose moieties are emphasized.

Analysis of the self-defense gene (fmrO) of a fortimicin A (astromicin) producer, Micromonospora olivasterospora: comparison with other aminoglycoside-resistance-encoding genes

The nucleotide (nt) sequence of a 3409-bp PvuII fragment carrying the self-defense gene (fmrO) of a fortimicin A (FmA; astromicin) producer, Micromonospora olivasterospora, was determined; four open reading frames (ORFs) exist in this region. Expression analysis of fmrO using the lac promoter in Escherichia coli revealed that ORF-3 encodes fmrO. ORF-1 was considered to encode a FmKH epimerase (fms11). ORF-2, ORF-3 and ORF-4 seemed to form an operon. No homology was detected between fmrO and the resistance-encoding gene fmrT of Streptomyces tenjimariensis, a producer of the Fm-group antibiotic, istamycin. Gene organization around the fmr genes differed considerably between M. olivasterospora and S. tenjimariensis. The deduced amino acid sequence of fmrO showed an identity of 30.8% to grmA of M. purpurea and 35.8% to grmB of M. rosea, respectively, suggesting that fmrO encodes a 16S rRNA methyltransferase. We found in M. purpurea a novel resistance gene distinct from grmA and highly similar to fmrO which conferred a resistance phenotype similar to that of fmrO. These results suggest that fmrO of M. olivasterospora and the two resistance-encoding genes of M. purpurea were derived from a common ancestral gene.

Synthesis of protected purpurosamine B and 6-epipurpurosamine B

In relation to the synthesis of antipseudomonal drugs, namely, gentamicin C2 and 3-de-O-methylsporaricin A, a protected purpurosamine B (15) and 6-epipurpurosamine B (13) were synthesized. The key intermediate, methyl 2,3,4,7- tetradeoxy-6-O-(methylsulfonyl)-2-phthalimido-beta-L-lyxo-++ +heptopyranoside (8), was obtained in 48% yield by Grignard addition to methyl 2,3,4-trideoxy-2-phthalimido-alpha-D-erythro-hexodialdo-1,5-pyrano side (7) proceeding in accordance with Cram's chelate rule, followed by methylsulfonylation. From 8, compound 15 was readily obtained by introduction of the azide group with inversion of configuration at C-6. Compound 13 was obtained by introduction of the azide group with retention of configuration.

Compound A49759, the 3-O-demethyl derivative of fortimicin A: in vitro comparison with six other aminoglycoside antibiotics

O-Demethylfortimicin A (compound A49759) was tested against 445 bacteria, and the results were compared with those obtained with fortimicin A, amikacin, gentamicin, netilmicin, sisomicin, and tobramycin. A49759 was found to be active and bactericidal against the Enterobacteriaceae, nonfermentative gram-negative bacilli, and Staphylococcus aureus. A49759 was two- to fourfold more active than fortimicin A against most species tested, but generally fourfold less active than amikacin against this population of Pseudomonas aeruginosa (85% inhibited at less than or equal to 16 microgram of amikacin per ml and 85% inhibited at less than or equal to 64 microgram of A49759 per ml). Only amikacin and A49759 were resistant to most aminoglucoside-inactivating enzymes and also had significant antipseudomonal activity. Amikacin was inactivated by aminoglycoside 6'-acetyltransferase, and A49759 was inactivated by aminoglycoside 3-acetyltransferase. The minimal inhibitory concentrations of all tested aminoglycosides were increased by augmenting the inoculum size.

In vitro and in vivo antimicrobial activities of sporaricin A, a new aminoglycoside

The in vitro and in vivo antimicrobial activity of sporaricin A, a new aminoglycoside, was compared with that of amikacin, dibekacin, and gentamicin. Sporaricin A showed a broad spectrum of activity against various gram-positive and -negative bacteria, including amikacin-, dibekacin-, or gentamicin-resistant strains. Sporaricin A inhibited more than 90% of clinical isolates of staphylococci, Klebsiella, Enterobacter, Citrobacter, Serratia, and Proteus, except for P. morganii and P. inconstans, at the concentration of 3.13 microgram/ml. This activity, except for that against Serratia, was similar to that of amikacin. Against P. inconstans and S. marcescens, sporaricin A was more effective than amikacin, dibekacin, and gentamicin. However, its activity against Pseudomonas aeruginosa was relatively weak in comparison with three other aminoglycosides. Sporaricin A was highly effective against bacteria that had various aminoglycoside-inactivating enzymes and that were resistant to the other drugs tested, but it was not active against those with aminoglycoside 3-acetyltransferase-I. The activity of sporaricin A tended to be greater with a reduction in inoculum size of bacteria and an increase in medium pH and decreased slightly in the presence of 10 to 50% horse serum. The in vitro activity was confirmed by in vivo tests in experimental infections with various bacteria. Its protective effect seemed to be equal to or greater than that of amikacin or dibekacin.