Enantiomeric separation of leucines

Structural characterization and bioactivity profiling of the fungal peptaibiotic tolypin reveal protective effects against influenza viruses

In a bioprospection for new antivirals, we tested nonribosomally biosynthesized polypeptide antibiotics in MDCK II cells for their actions on influenza A and B viruses (IAV/IBV). Only tolypin, a mixture of closely related 16-residue peptaibiotics from the fungus Tolypocladium inflatum IE 1897, showed promising activity. It was selected for further investigation and structural characterization by ultrahigh performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HR-MS/MS) and ultrahigh performance liquid chromatography coupled to in-source collision-induced dissociation tandem mass spectrometry (UHPLC-isCID-HR-MS/MS), revealing 12 partially co-eluting individual peptides that were fully sequenced. Since tolypin-related efrapeptins are potent inhibitors of F1/Fo-ATPase, we screened tolypin for its toxicity against MDCK II cells and larvae of the greater wax moth Galleria mellonella. We found that a nontoxic concentration of tolypin (1 µg/mL) reduced the titer of two IBV strains by 4-5 log values, and that of an H3N2 strain by 1-2 log values, but the H1N1pdm strain was not affected. The higher concentrations of tolypin were cytostatic to MDCK II cells, shifted their metabolism from oxidative phosphorylation to glycolysis, and induced paralysis in G. mellonella, supporting the inhibition of F1/Fo-ATPase as the mode of action. Our results lay the foundations for future work to investigate the interplay between viral replication and cellular energy metabolism, as well as the development of drugs that target host factors.

Sequences of Tolypins, Insecticidal Efrapeptin-Type Peptaibiotics from Species of the Fungal Genus Tolypocladium

A peptide mixture named tolypin, originally isolated from species of the fungal genus Tolypocladium, was structurally characterised and sequences compared to those reported for efrapeptins isolated from strains of Tolypocladium inflatum. Chiral amino acid analysis, direct infusion, and online HPLC electrospray ionization tandem mass spectrometry provided composition, molecular weights of peptides, and series of diagnostic fragment ions. Sequences deduced from ESI-MS revealed that tolypins C-G are identical to efrapeptins C-G. The results were corroborated by ESI-MS and HPLC of an authentic efrapeptin sample from Eli Lilly Research Laboratories (USA). Comparison of the HPLC elution profiles of efrapeptin and tolypin indicated a pronounced microheterogeneity of the former. A high-resolution HPLC of authentic efrapeptin has not been published before. Close relationship and partial identity of sequences of tolypins and efrapeptins, which had previously been postulated, were definitely proven. The geographical origin of the two most important T. inflatum strains used for sequencing of efrapeptins/tolypins could unambiguously be clarified. A new minor compound, designated tolypin H1, was sequenced. High proportions of helicogenic Aib (α-aminoisobutyric acid) and l-isovaline, N-terminal acetyl-l-pipecolic acid and the unusual, amide-bound C-terminal residue, named (S)-2-amino-1-(1,5-diazabicyclo[4.3.0]non-5-ene-5-ylium)-4-methylpentane corresponding to 1-[(2S)-2-amino-4-methylpentyl]-2,3,4,6,7,8-hexahydropyrrolo[1,2-a]pyrimidin-1-ium, define these peptides as linear, cationic peptaibiotics.

Liquid chromatographic determination of D- and L-amino acids by derivatization with o-phthaldialdehyde and N-isobutyryl-L-cysteine. Applications with reference to the analysis of peptidic antibiotics, toxins, drugs and pharmaceutically used amino acids

In order to evaluate and extend the applicability of an analytical method that enables the quantitative and simultaneous high-performance liquid chromatographic determination of D- and L-amino acids (DL-AAs) by automated precolumn derivatization with o-phthaldialdehyde together with the chiral thiol N-isobutyryl-L-cysteine [J. Chromatogr., 666 (1994) 259] selected natural and synthetic bioactive peptides, as well as pharmaceutically used formulations of AA, were investigated and the amounts of D- and L-AA determined by fluorescence detection. Peptides containing cys(e)ine were oxidized with performic acid prior to hydrolysis with 6 M HCl, and those containing Trp were hydrolyzed with 4 M methanesulfonic acid (24 h at 110 degrees C in both cases). Peptides analyzed were the peptide antibiotics bacitracin, gramicidins A and S, polymyxin B, metanicin C, the peptide toxin malformin A and the peptide drugs D-Arg-[Hyp3,Thi5,8,D-Phe7]-bradykinin, beta-casomorphin and alpha s1-exorphin. Further, the enantiomeric ratios of pharmaceutically used AA formulations containing racemic DL-Ser, DL-Asp and DL-Met were determined, and the AA drugs L-Asp and L-Trp were tested negatively for the presence of the respective D-enantiomers. In two aqueous formulations of L-AA used for parenteral nutrition, low amounts of D-AA (0.1-0.9% with respect to certain L-AA enantiomers and of totally 128 mg and 149 mg D-AAs per liter infusion solution) were determined.

Beauverolides L and La from Beauveria tenella and Paecilomyces fumosoroseus

New beauverolides L and La were isolated and identified from the entomopathogenic fungi, Beauveria tenella and Paecilomyces fumosoroseus. Their structures, cyclo-[3-hydroxy-4-methyldecanoyl-L-phenylalanyl-L-alanyl-D-leucyl ], and cyclo-[3-hydroxy-4-methyldecanoyl-L-phenylalanyl-L-alanyl-D-allo-i soleucyl] were deduced from HPLC and GC-mass spectrometric analyses of their hydrolysates and NMR and mass spectral data.

Enantiomeric derivatization for biomedical chromatography

Derivatization reactions aimed at creating the basis for the chromatographic resolution of biologically and pharmaceutically important enantiomers are reviewed, with emphasis on the literature published in the last 10 years. Three main aspects of chiral derivatization are discussed. (a) Enantiomers containing suitable functional groups (amino, carboxyl, hydroxyl, epoxy, etc.) are transformed into covalently bonded diastereomeric derivatives using homochiral derivatizing agents. The diastereomers formed (esters, amides, urethanes, urea and thiourea, etc., derivatives) can be separated on achiral stationary phases. The derivatization reactions often afford further advantages, such as the improvement of chromatographic properties and the detectability of the solutes using UV and fluorimetric detectors. (b) Covalent but achiral derivatization is often necessary even with the use of chiral stationary phases enabling in principle direct enantioseparations (Pirkle-type columns, cyclodextrin-bonded phases, glycoprotein column and functionalized cellulose columns). The main goals of these derivatization reactions (which are analogous to those discussed above), are to introduce functional groups into the molecule of the enantiomers that improve the possibilities for chiral interactions or block functional groups to avoid non-specific interactions. (c) In the broader sense, the dynamic formation of diastereomers using chiral mobile phase additives (cyclodextrins, various reagents to form diastereomeric ion pairs, adducts, mixed metal complexes) can also be considered to be chiral derivatization reactions and is therefore briefly discussed also.

Resolution of enantiomers of amino acids by HPLC

Application of HPLC as a prime tool in the area of enantiomeric resolution has opened doors of success and varied interest. Use of chiral reagents either indirectly (as derivatization reagent) or directly (added to stationary or mobile phase) has led to achieve resolution of a wide range of compounds. Amino acids, being important molecules with simple structure and easy availability, have been extensively studied. A bibliographic survey on HPLC resolution of amino acids and derivatives along with a brief discussion on general methods of enantiomeric separation has been presented.

Chiral separation by high performance liquid chromatography. I. Review on indirect separation of enantiomers as diastereomeric derivatives using ultraviolet, fluorescence and electrochemical detection

The increased attention on the therapeutic implications of stereoisomerism has provided an impetus for the development of analytical methods for enantiomeric separation. The indirect method of separation of enantiomers as diastereomers using high performance liquid chromatography (HPLC) has emerged as an efficient and versatile approach. This is due mainly to the availability of numerous chiral derivatization reagents (CDRs). This article reviews CDRs useful for the development of an indirect HPLC method using ultraviolet, fluorescence and electrochemical detection. In addition, factors crucial for the development of the indirect method are discussed.

Morphological alterations accompanying the effect of peptaibiotics, α-aminoisobutyric acid-rich secondary metabolites of filamentous fungi, on Culex pipiens larvae

The effect of different representatives of the group of peptaibiotics, alpha-amino-isobutyric acid rich secondary metabolites of filamentous fungi, on Culex pipiens larvae was studied. Light and transmission electron microscopy techniques were used to localize the intracellular damage and to determine the target organells for the mode of action of peptaibols in mosquito larvae. Though different in insecticidal activity, all tested compounds induced the same type of tissue damage, which was characterized by heavy challenge of mitochondria followed by partial swelling, crystaeolysis and destruction of mitochondrial walls. It is concluded that the mode of action of peptaibols in mosquito larvae is mediated through the damage of mitochondria. The structure-mosquitocidal effect of these compounds, their potential mode of action and role in the natural fungal entomopathogenic process are briefly discussed.