WYE-120318, a ring contraction product of methylnaltrexone, and structure revision of coniothyrione.

A contracted ring degradation product, WYE-120318 (compound 2), was discovered during the development phase for methylnaltrexone bromide (compound 1) drug substance. The compound was isolated by high-performance liquid chromatography fractionation, and its structure was determined by spectroscopic data analyses. WYE-120318 is formed from methylnaltrexone through a benzyl-benzilic acid type rearrangement reaction to yield an α-hydroxy-cyclopentanecarboxylic acid substructure. The proposed structure and the formation mechanism are confirmed by the synthesis of WYE-120318 from methylnaltrexone (compound 1). A similar benzyl-benzilic acid type rearrangement reaction can be envisioned as the biological origin of remisporine A (compound 3), a naturally occurring cyclopentadienyl compound that autocatalytically dimerizes to remisporine B (compound 4). The structure of remisporine A was deduced from its dimer 4. Coniothyione (compound 5) can be considered as the first example of a stable natural product bearing the remisporine A skeleton. However, the regiochemistry of the chlorosubstitution in the coniothyrione structure needs to be revised to compound 6 on the basis of the nuclear magnetic resonance data and biogenesis analysis.

Structural characterization of the tobramycin-piperacillin reaction product formed at pH 6.0.

Tobramycin is an aminoglycoside antibiotic that loses a significant amount of activity in the presence of Zosyn at pH 6. As part of our investigation into ways to improve the compatibility of tobramycin with Zosyn (which contains piperacillin and tazobactam in an 8:1 ratio buffered at pH 6 by sodium citrate) by lowering the pH, we identified the reaction product of tobramycin and piperacillin at pH 6.0 and the order of the pK(a) values of tobramycin. The structure of the main reaction product of tobramycin and piperacillin at pH 6.0 was determined by 2D NMR to be the product of 3″-NH(2) reacting with the ß-lactam of piperacillin. The order of the pK(a) values of the nitrogens of tobramycin was determined by (1)H and (15)N NMR titrations to be 6'-NH(2)>2'-NH(2)>1-NH(2)≈3″-NH(2)>3-NH(2). At pH 4.0, the reaction between tobramycin and Zosyn was almost negligible for a period of up to 2 h. The pH can be lowered by adding an acid such as HCl or citric acid to Zosyn to make a pH 4.0 buffer.

Isolation and structure of homotemsirolimuses A, B, and C.

Homotemsirolimuses A, B, and C (2a, 2b, 2c) were found to be minor components of a temsirolimus preparation made from rapamycin. These three temsirolimus analogues are derived from the corresponding rapamycin analogues, homorapamycins A, B, and C (1a, 1b, 1c) produced by the strain Streptomyces hygroscopicus. The structures of homotemsirolimuses A, B, and C were determined by spectroscopic methods. These compounds were tested for mTOR kinase inhibition and in two proliferation assays using LNCap prostate and MDA468 breast cancer cells. The results suggested that the mTOR inhibition and antiproliferation potencies for 2a, 2b, and 2c are comparable to those of rapamycin (1) and temsirolimus (2).

Design and synthesis of HCV agents with sequential triple inhibitory potentials.

The union of HCV-796, a potent selective HCV NS5B polymerase inhibitor, and Ribavirin, a molecule with activities against a wide spectrum of viruses, resulted in a class of new anti-HCV agents with a sequential triple inhibitory mechanism.

Synthesis and SAR of novel 4-morpholinopyrrolopyrimidine derivatives as potent phosphatidylinositol 3-kinase inhibitors.

Significant evidence suggests that deregulation of the PI3K/Akt pathway is important in tumor progression. Mechanisms include loss of function of the tumor suppressor PTEN and high frequency of mutation of the PI3K p110alpha isoform in human malignancies. This connection between PI3K and tumor genesis makes PI3K a promising target for cancer treatment. A series of 4-morpholinopyrrolopyrimidine derivatives were synthesized and evaluated as inhibitors of PI3Kalpha and mTOR, leading to the discovery of PI3Kalpha selective inhibitors (e.g., 9) and dual PI3Kalpha/mTOR kinase inhibitors (e.g., 46 and 48). PI3Kalpha/mTOR dual inhibitors demonstrated inhibition of tumor cell growth in vitro and in vivo and caused suppression of the pathway specific biomarkers [e.g., the phosphorylation of Akt at Thr308 (T308) and Ser473 (S473)] in the human breast cancer cell line MDA361. In addition, compound 46 demonstrated good in vivo efficacy in the MDA361 human breast tumor xenograft model.

Structure characterization of lipocyclopeptide antibiotics, aspartocins A, B & C, by ESI-MSMS and ESI-nozzle-skimmer-MSMS.

Three lipocyclopeptide antibiotics, aspartocins A (1), B (2), and C (3), were obtained from the aspartocin complex by HPLC separation methodology. Their structures were elucidated using previously published chemical degradation results coupled with spectroscopic studies including ESI-MS, ESI-Nozzle Skimmer-MSMS and NMR. All three aspartocin compounds share the same cyclic decapeptide core of cyclo [Dab2 (Asp1-FA)-Pip3-MeAsp4-Asp5-Gly6-Asp7-Gly8-Dab9-Val10-Pro11]. They differ only in the fatty acid side chain moiety (FA) corresponding to (Z)-13-methyltetradec-3-ene-carbonyl, (+,Z)-12-methyltetradec-3-ene-carbonyl and (Z)-12-methyltridec-3-ene-carbonyl for aspartocins A (1), B (2), and C (3), respectively. All of the sequence ions were observed by ESI-MSMS of the doubly charged parent ions. However, a number of the sequence ions observed were of low abundance. To fully sequence the lipocyclopeptide antibiotic structures, these low abundance sequence ions together with complementary sequence ions were confirmed by ESI-Nozzle-Skimmer-MSMS of the singly charged linear peptide parent fragment ions H-Asp5-Gly6-Asp7-Gly8-Dab9-Val10-Pro11-Dab2(1+)-Asp1-FA. Cyclization of the aspartocins was demonstrated to occur via the beta-amino group of Dab2 from ions of moderate intensity in the ESI-MSMS spectra. As the fatty acid moieties do not undergo internal fragmentations under the experimental ESI mass spectral conditions used, the 14 Da mass difference between the fatty acid moieties of aspartocins A (1) and B (2) versus aspartocin C (3) was used as an internal mass tag to differentiate fragment ions containing fatty acid moieties and those not containing the fatty acid moieties. The most numerous and abundant fragment ions observed in the tandem mass spectra are due to the cleavage of the tertiary nitrogen amide of the pipecolic acid residue-3 (16 fragment ions) and the proline residue-11 (7 fragment ions). In addition, the neutral loss of ethanimine from alpha,beta-diaminobutyric acid residue 9 was observed for the parent molecular ion and for 7 fragment ions.

Polyene antibiotics from Streptomyces mediocidicus.

Three polyene antibiotics, mediomycins A (1), B (2), and clethramycin (3), were isolated from Streptomyces mediocidicus ATCC23936. Their structures were elucidated through extensive NMR study coupled with chemical reactions and MS/MS fragmentation analysis. All three compounds are linear polyenes consisting of a conjugated oxo-triene group and a hexaene moiety. Compounds 1 and 2 are new polyenes. All three compounds demonstrated a broad spectrum of antifungal activity in vitro.

Septocylindrins A and B: peptaibols produced by the terrestrial fungus Septocylindrium sp. LL-Z1518.

Two new peptaibols, septocylindrin A (1) and septocylindrin B (2), related to the well-studied membrane-channel-forming peptaibol alamethicin, were obtained from a terrestrial isolate of the fungus Septocylindrium sp. Both 1 and 2 are linear 19-amino acid peptides with a modified phenylalanine C-terminus. Analysis of the HRMS data indicated that they differ only in the 18th residue, where 1 contains Glu and 2 contains Gln. The structures of these two peptaibols were determined by extensive NMR and HRMS analysis. The absolute configurations of amino acids present in 1 were determined using Marfey's methodology. Both compounds were isolated through bioassay-guided fractionation and exhibited significant antibacterial and antifungal activity.

Hygrocins a and B, naphthoquinone macrolides from Streptomyces hygroscopicus.

Two new naphthoquinone macrolides, hygrocins A (1) and B (2), were isolated from the fermentation broth of Streptomyces hygroscopicus. Hygrocin A is not stable due to the presence of an active methylene group (C-22), which undergoes intramolecular aldol condensation with the quinone ring to yield a gamma-lactam derivative, 6. Its structural elucidation was achieved by chemical conversion to 3, an unusual diazomethane derivative, and confirmed by its alkaline hydrolysis product 4, hydrogenation derivative 5, and "degradation" product 6. The structure of hygrocin B was determined by combined chemical and spectroscopic methods.

Pseudopyronines A and B, alpha-pyrones produced by a marine Pseudomonas sp. F92S91, and evidence for the conversion of 4-hydroxy-alpha-pyrone to 3-furanone.

In our search for inhibitors of bacterial fatty acid biosynthesis, two new alpha-pyrones, pseudopyronines A (1) and B (2), were isolated from a marine Pseudomonas sp. F92S91. The naturally occurring alpha-pyrones appeared to be unstable, evidenced by the conversion of pseudopyronine B into an oxidation product, 3-furanone (3). Structural elucidations were made by spectroscopic analyses including 2D-NMR data.

Structure determination of glycinocins A to D, further evidence for the cyclic structure of the amphomycin antibiotics.

Four novel cyclolipopeptides, glycinocins A to D, were isolated from the fermentation broth of an unidentified terrestrial Actinomycete species. These compounds were separated and purified from the fermentation broth by 1-butanol extraction, followed by repeated reversed-phase HPLC. Their structures were elucidated by spectroscopic and chemical degradation studies. The absolute configuration of the amino acid residues was determined using Marfey's methodology. The glycinocin antibiotics are structurally related to amphomycin that was originally reported as a linear lipopeptide with C-terminal diketopiperazine moiety. Our degradation study of the glycinocin antibiotics also yielded diketopiperazine-containing fragments, but these have been shown to be hydrolytic by-products generated by condensation of the pipecolinic acid and diamino propionic acid residues.

Novel alpha-pyrones produced by a marine Pseudomonas sp. F92S91: taxonomy and biological activities.

Inhibitors of the enzymes involved in fatty acid biosynthesis (FAB) have been reported as antibacterial agents. These include thiolactomycin, cerulenin, triclosan, diazoborine, naphthyridinones, aminopyridines and pyridoindoles. Our search for new FAB inhibitors, using a lacZ reporter cell-based screen, led to several confirmed hits. Culture F92S91, later identified as a Pseudomonas sp. based on 16S profiling, was found to produce two alpha-pyrones (I and II) and three high molecular weight peptides. The pyrones were unstable under acidic conditions, and they were rearranged into a furanone derivative (III). Of these compounds, pyrone I was the most active with MICs (microg/ml) against B. subtilis (1 to approximately 2), MRSA (2 to approximately 4), M. catarrhalis (4) and VRE (2 to approximately 64). Effects on macromolecular synthesis and membrane functions were tested in B. subtilis. Pyrone I nonspecifically inhibited incorporation of radiolabeled precursors into DNA, RNA and protein within 5 minutes of drug exposure, similar to that of triclosan. Both compounds also inhibited the cellular uptake of these precursors. Cerulenin did not have an effect until 30 minutes of drug treatment. Pyrone I and triclosan were membrane-active (BacLight test); however, pyrone I (at < or = 128 microg/ml concentration) was not hemolytic to human RBCs in contrast to triclosan, which was hemolytic at 16 microg/ml. These data suggest that pyrone-I, unlike triclosan, selectively affects bacterial membrane function.