Strains of Stenotrophomonasmaltophilia R3089, isolated from the rhizosphere of rape plants (Brassica napus L.), produced a novel antifungal compound,namedmaltophilin, which inhibited the growth of various saprophytic, human-pathogenic and phytopathogenic fungi but was inactive against Gram-positive and Gram-negative bacteria. Maltophilin is a novel macrocyclic lactam antibiotic with a molecular massof 510mu.The compound wasisolated from the culture nitrate by ethyl acetate extraction and gel filtration on Sephadex LH20and purified by preparative HPLC on reversed phase. The structure of maltophilin was elucidated by electrospray mass spectrometry and XHand 13C NMRspectroscopy.
Rhizoferrin is a member of a new class of siderophores (microbial iron transport compounds) based on carboxylate and hydroxy donor groups rather than the commonly encountered hydroxamates and catecholates. We have studied the coordination chemistry of rhizoferrin (Rf), as a representative of this group, with Fe(3+), Rh(3+), Cr(3+), Al(3+), Ga(3+), VO(2+), and Cu(2+). The metal complexes have been studied by UV-vis, CD, NMR, and EPR spectroscopies and mass spectrometry. The formation constants for the iron complex have also been measured and yield a log K(LFe) of 25.3. The Rh and Cr rhizoferrin complexes are unusual in that they appear to adopt a chirality about the metal center that is the opposite of the native iron analog. Several of the alternative metal ion complexes are found to have biological activity toward Morganella morganii in a plate type assay.
COMMUNICATIONS 4a: 1 (473 mg, 1.8 mmol), 3 (430 mg, 1.8 mmol), and bis(triphenylphosphane1-(ethene)platinum (83 mg, 0.12 mmol, 6.2 mol%) in toluene (15 mL) were heated under reflux for 24 h. Afterwards, the precipitate was isolated by filtration, washed several times with THF and CH,Cl,, and dried in vacuum. Yield: 455 mg (50.6%)) m.p.: >310"C, 'HNMR (ZOOMHz, [D,]MeOH): 6 =6.5-6.9 (m); I3C NMR (50 MHz, [DJMeOH): 6 = 146.3,120.9, 116.4(C6H.,), CBnot observed; "BNMR (64 MHz, [DJMeOH): 6 = 34 (Av,,~ = 524 Hz), 18 (AvIj, = 58 Hz, C,H,02BOCD,); HR-MS (EI): m/z 500.1209 ( M + , calcd '2C,,1H,,'oB,'60,: 500.1217); correct C, H analysis. 2b, 2c: A suspension of 2a (785 mg, 1 mmol) in toluene (15 mL) and methyllithium (8 mL of a 1.5 M solution in diethyl ether, 12 mmol) was first stirred for 1.5 h at -5 "C and then for 8 h at 25 "C. After removing the insoluble components, a yellow solution of 2b was obtained which contained minor amounts of boranates. I I B 29 Hz); GC-MS: m/z ("A) 317 (100) [M+], 302 (17.4) [ M + -Me], 41 (92.4) [BMe,+]. An excess of pyridine was added to the yellow solution. Crystalline 2c precipitated from the resulting orange-red solution at room temperature. Yield: 296 mg(33%), m.p.: >250°C (decomp), 'HNMR (200 MHz, CDCI,): 6 = -0.3 to 0.3 (m, BMe), 5.8 -6.9 (m, C,H,), 7.0 (m, Py), 7.5 (m, Py), 8.2 (m, Py); 13C NMR (50MHz, CDCI,): 6 =13.0 (BMe, br), 114.6, 116.5, 118.2, 120.0, 153.6, 160.0 (C6H,), 123.7, 136.6, 149.6 (Py), 168.0 (CB, br); I l B NMR (64 MHz, CDCI,): 6 = 0.3 ( A V , ,~ = 204 Ht); MS (FD): m/z 982 [ M + -Py -4Mel. NMR (64 MHz): 6 = 6 (AVlj2 = 466 Hz), -17.4 (Av,,, = 87 Hz), -20.6 (AVlj2 =
Epidermin, a tetracyclic peptide antibiotic with therapeutic activity against acne, is produced by the Gram-positive bacterium Stupliylococcus epidermidis. It contains the uncommon amino acids 2,3-didehydroaminobutyric acid, meso-lanthionine, [j-methyllanthionine, and C-terminal S-[ (Z)-2-aminovinyl]-D-cysteine.l*l The prepeptide EpiA. consisting of 52 amino acids, is synthesized ribosomally and transformed into the biologically active 22mer peptide by posttranslational modifications. These modification reactions comprise oxidative decarboxylation, dehydration, formation of four thioether bridges, and cleavage of the leader peptide"] (Fig. 1). Complementation studies of epidermin-negative mutants and DNA sequencing have revealed that the genes q i B , epic, epiD, and (.pip encode the enzymes for the biosynthesis of epidermin.i31 The enzyme EpiD has been isolated and characterized. In this novel Epidermin Fig. I . Model of the biosynthesis of epiderinin. The ribosomiilly syiithesizcd pi-epcptide EpiA is converted into the anttmicrobislly iictivc. teti-acyclic laiitibiotic epidermin by the following posttranslational modi!ications -a ) oxidatire decarboxylation of the C-terminal cysteine residue. hj dehydration of serine and threoninc residues, c) formation of thioether bridges (lanthionine atid /~-mKthyllanthioniiiej. atid d) cleavage of the leader peptide (30 residues). Abu = 2-aininohutyric acid; Dhb = r,P-drdehydrobutyric acid; cysteine residues iirr shaded in gray. has not yet been studied in detail, it can be assumed that the first step is the oxidation leading to the formation of the double bond followed by decarboxylation to form the thioen~l.[~I Flavin coenzyme that has been reduced during the reaction is reoxidized probably by aerial oxygen.The substrate specificity of the new enzyme has been investigated by using synthetic peptides and peptide libraries. The MS-MS fragmentation pattern of the substrate Ser-Phe-Asn-Ser-Tyr-ThrCys after reaction with EpiD revealed that only the C-terminal cysteine was modified, presumably by conversion into a C-terminal thioenol by oxidative decarboxylation. In this paper, we report on the structure determination of the product of this unusual enzymatic reaction.The heptapeptide SFNSYTC was prepared by solid-phase synthesis with fluorenylmethoxycarbonylitert-butyl protecting groups.[81 After treatment with 5,5'-dithiobis(2-nitrobenzoic acid) (Ellman's reagent). both the purified peptide and the peptide modified by EpiD showed an increase in molecular mass by 197 Da in the electrospray ionization mass spectrum (ESI-MS). This corresponds to the formation of asymmetric disulfides from the thiol groups of the peptide and of 5-thio-2-nitrobenzoic acid. These disulfides could be reduced by addition of Mpropanethiol and partly converted into the asymmetric disulfide with /~-propanethiol. The addition of Ellman's reagent to the assumed double bond in the product, which would lead to an increase in molecular mass by 199 Da. has not been observed.Previous two-dimensional N M R exper...
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