Kirk Marat

Synthesis of 20α- and 20β-acetamido, amino, nitro and hydroxy derivatives of 14-hydroxy-5β,14β-pregnane 3β-glycosides: pregnanes that bind to the digitalis receptor

Synthesis of 20α- and 20β-acetamido-, amino-, nitro- and hydroxy-3β-glycoside (α-L-rhamnopyranoside and tris-β-D-digitoxoside) and genin derivatives of 14-hydroxy-5β,14β-pregnane together with the C-20 oxime, hydrazone and amidinohydrazone is described from digitoxin. Ortho esters were also isolated. Structures were established by NMR measurements. These compounds have been shown to bind to the digitalis receptor of heart muscle. The 20β derivatives were consistently more potent than are the corresponding 20α compounds. The 20β-nitro α-L-rhamnoside derivative proved to be the most potent. Receptor binding data are given and structure-activity relationships are presented.

The Implications of (2S,4S)‐Hydroxyproline 4‐O‐Glycosylation for Prolyl Amide Isomerization

The conformations of peptides and proteins are often influenced by glycans O-linked to serine (Ser) or threonine (Thr). (2S,4R)-4-Hydroxyproline (Hyp), together with L-proline (Pro), are interesting targets for O-glycosylation because they have a unique influence on peptide and protein conformation. In previous work we found that glycosylation of Hyp does not affect the N-terminal amide trans/cis ratios (K(trans/cis)) or the rates of amide isomerization in model amides. The stereoisomer of Hyp--(2S,4S)-4-hydroxyproline (hyp)--is rarely found in nature, and has a different influence both on the conformation of the pyrrolidine ring and on K(trans/cis). Glycans attached to hyp would be expected to be projected from the opposite face of the prolyl side chain relative to Hyp; the impact this would have on K(trans/cis) was unknown. Measurements of (3)J coupling constants indicate that the glycan has little impact on the C(gamma)-endo conformation produced by hyp. As a result, it was found that the D-galactose residue extending from a C(gamma)-endo pucker affects both K(trans/cis) and the rate of isomerization, which is not found to occur when it is projected from a C(gamma)-exo pucker; this reflects the different environments delineated by the proline side chain. The enthalpic contributions to the stabilization of the trans amide isomer may be due to disruption of intramolecular interactions present in hyp; the change in enthalpy is balanced by a decrease in entropy incurred upon glycosylation. Because the different stereoisomers--Hyp and hyp--project the O-linked carbohydrates in opposite spatial orientations, these glycosylated amino acids may be useful for understanding of how the projection of a glycan from the peptide or protein backbone exerts its influence.

A 31p and 15N NMR study of the extraction of uranyl nitrate by Di-2-ethylhexyl phosphoric acid

Low temperature 31P and 15N NMR spectroscopy was used to investigate the species forming in the organic layer following the extraction of uranium from nitric acid solutions with di-2-ethylhexyl phosphoric acid. It was found that uranium is extracted from neutral solutions as the 1:2 complex UO2A2 regardless of what anion is present. For dilute nitric acid solutions, the uranium is extracted both as associated and mixed nitrato species. As the nitric acid concentration of the aqueous layer increases, the mixed nitrato complex, UO2(NO3)A·HA, becomes predominant.

Antimicrobial activities of the CH2Cl2–CH3OH (1 : 1) extracts and compounds from the roots and fruits of Pycnanthus angolensis (Myristicaceae)

This study was designed at evaluating the antimycobacterial, antibacterial and antifungal activities of the CH2Cl2–CH3OH (1 : 1) extracts and isolated compounds, namely 3,4-dimethoxy-3′,4′-methylenedioxy-7,7′-epoxylignan (1), genkwainin (2), pycnanthulignene C (3), 4,5-dimethoxy-3′,4′-methylenedioxy-2,7′-cycloligna-7,7′-diene (4), pycnanthulignene A (5) from the roots, and calycosin (6), biochanin A (7) and prunetin (8), from the fruits of Pycnanthus angolensis. The microplate alamar blue assay and the broth microdilution method were used to determine the minimal inhibitory concentration (MIC) and minimal microbicidal concentration of the samples. The H+-ATPase-mediated proton pumping assay was used to evaluate one of the possible mechanisms of action of the extracts and isolated compounds. The results of MIC determinations showed that the extract from roots was able to prevent the growth of all the studied organisms, including mycobacteria, fungi, and Gram-positive and Gram-negative bacteria. All tested compounds showed antimicrobial activities to different extents, compound 1 and 8 exhibiting the best antimicrobial spectrum, with 92.3% of the tested organisms being sensitive. The results obtained in this study also showed that the extracts as well as most of the compounds were able to inhibit the H+-ATPase activity. The overall results provided evidence that P. angolensis and some of its components might be potential sources of antimicrobial drugs against tuberculosis, bacterial and fungal diseases.

Structural characterization of two novel oxidative derivatives of cyclosporine generated by a chemical method.

OBJECTIVES To study the generation of cyclosporine derivatives (CMs) by chemical oxidation of the parent compound using hydrogen peroxide. METHODS AND RESULTS Hydrogen peroxide was added to cyclosporine (CsA), which was dissolved in ether. After liquid-liquid extraction, CMs were purified by high performance liquid chromatography (HPLC). Detailed structures of CMs were determined by fast atomic bombardment mass spectrometry (FABMS) and nuclear magnetic resonance spectroscopy (NMR). Our results indicated that the parent compound was modified at amino acid number 1 by hydroxylation of the carbon and the formation of a tetrahydrofuran five member ring structure. In addition, these two oxidative products of CsA were determined to be isomeric to each other, differing only in the configuration at one or more carbon atoms. This modification is in contrast to that observed for the formation of the cyclic metabolite of CsA, namely AM1c, by cytochrome P-450 isoenzymes, where the addition of the hydroxyl group occurs on the carbon of amino acid 1. CONCLUSION 3 to 4 mg of 2 oxidative derivatives could be produced from 5 mg of CsA by chemical modification of the parent compound. In comparison, biotransformation using the drug-induced hepatic microsomal enzyme system could only produce 0.5 to 1 mg of metabolites/derivatives from 5 mg of CsA.

Zinc–acetic acid reduction of the steroid 4-en-3-one: novel conversion of the 4-en-3-one into the 2-en-4-one via a vinyl chloride

Transposition of a steroid 4-en-3-one to the 2-en-4-one has been carried out. 4-Chlorotestosterone acetate on Zn–HOAc reduction yields a mixture of the C-5 epimers of the 4-chloro-3-ene together with a C-3 dimer. The vinyl chlorides, after epoxidation followed by rearrangement and elimination, give the 2-en-4-one. A synthesis of 17β-hydroxy-5α-androst-2-en-4-one and 17β-hydroxy-5α-estr-2-en-4-one is described.

Electron-coupled through-space or fragment spin-spin coupling between 19F nuclei

The indirect spin-spin coupling constants over four formal bonds between fluorine nuclei in 2-fluoro-5-nitrobenzotrifluoride, 2,5-difluorobenzotrifluoride, pentafluorobenzoyl fluoride, and 2-fluoro-6-chlorobenzoyl fluoride, are +12.94 ± 0.02, +13.0 ± 0.1, +38.8 ± 0.1, and +30.6 ± 0.1 Hz, respectively. These “through-space” or “fragment” interactions are compared with previous sign and magnitude measurements and are in agreement with two semiempirical theories.

Synthesis and isomerization of 19-hydroxy-5β,19-cyclosteroids

Abstract Synthesis of 19(R/S)-hydroxy-5β,19-cycloandrostane-3,17-dione by reductive cyclization of the steroid 4-en-3-one 19-aldehyde with zinc in aqueous acetic acid is reported. On either acid or base treatment the R-isomer is converted to the S-isomer through an intermediate 3-hydroxy-3,5-cyclosteroid.

A Convenient Hydroxylation

Abstract In connection with the introduction of hydroxy functions to the C-7 and C-9 positions of anthracycline antitumor antibiotics, 3 such as 4-demethoxydaunomycin (1)3 and of the hetero-anthracyclines such as 4-demethoxy xanthodaunomycin (2), 4-demethoxy thioxantho-daunomycin (3) and 4-demethoxy sulfoxodaunomycin (4), we have discovered that for the hetero-anthracycline series4 the dihydroxylation can be done in one step instead of a multi-step sequence as in the anthracycline series5. However, in the case of hetero-iso-anthracycline series4, ring D was aromatized under the same dihydroxylation condition. Thus, in a typical experiment, xanthone (5) (1.3 g) was added to a solution of anhydrous N,N-dimethylformamide (150 ml) and t-butyl alcohol (30 ml).

Difluoro [2.2] paracyclophanes Characterization by 1H, 13C and 19F NMR

Abstract The four isomers of difluoro[2.2]paracyclophane are uniquely identified on the basis of their 1 H, 13 C and 19 F NMR spectra. 13 C/ 12 effects on the 19 F chemical shifts were measured and a small transannular effect was detected.