Jerry L. Dallas

Design, synthesis, and in vitro biological activity of benzimidazole based factor Xa inhibitors

Inhibitors based on the benzimidazole scaffold showed subnanomolar potency against Factor Xa with 500-1000-fold selectivity against thrombin and 50-100-fold selectivity against trypsin. The 2-substituent on the benzimidazole ring had a strong impact on the FXa inhibitory activity. Crystallography studies suggest that the 2-substituent may have a conformational effect favoring the extended binding conformation.

Mg-2,4-divinyl pheoporphyrin a5: the product of a reaction catalyzed in vitro by developing chloroplasts.

The major product of an aerobic reaction mixture containing developing chloroplasts, Mg-protoporphyrin IX, S-adenosylmethionine, and other cofactors was isolated and purified. Structural studies using nuclear magnetic resonance confirmed earlier reports, based on fluorescence and absorption spectra, that this compound is Mg-2,4-divinyl pheoporphyrin a5. The molecular weight determined by secondary-ion mass spectroscopy further confirmed the assigned structure. Absorption and fluorescence spectra indicate that this compound is identical to that reported previously by various workers in less-purified biological extracts. The nuclear magnetic resonance spectrum of the Mg-free base also supports the assigned structure.

Identification of a key structural feature of cobalt(III)-bleomycins: an exogenous ligand (e.g. hydroperoxide) bound to cobalt.

A series of cobalt(III) complexes of the anticancer antibiotic bleomycin has been prepared. Mass spectrometry and enzymatic analysis show that the green cobalt-bleomycin complex contains a hydroperoxide (-OOH) group bound to cobalt with unusual stability. Under appropriate conditions, cobalt-bleomycins containing other monodentate ligands to cobalt can be formed; fast-atom bombardment mass spectra of such complexes show peaks for cobalt-bleomycin at the expected mass, and also peaks for the intact complexes at the required higher mass.

Pulse Fourier transform water suppression and underwater decoupling in aqueous solutions

Abstract A pulse Fourier transform NMR double-resonance technique is described for simultaneous water suppression and underwater decoupling in 90 to 95% H2O solutions. Suppression of the intense water resonance is achieved via saturation with a selective pulse from the observe rf transmitter. This long soft pulse is applied prior to the nonselective acquisition pulse and is phase shifted from its initial phase by 180° on alternate scans. A requirement of the method, then, is that the observe rf transmitter be capable of switching from a low-power (∼1 W) to a high-power (∼100 W) mode of operation under computer control. Decoupling is achieved with a time-shared homonuclear decoupling field whose rf phase is also shifted by 180° on alternate scans. Spectrometer adjustments which, if not taken into consideration, impede the routine application of the technique, are discussed.

1D and 2D NMR of nanocellulose in aqueous colloidal suspensions

This is the first report on surface structural elucidation of individual nanocellulose as colloidal suspensions by 1D 1H, 2D heteronuclear single quantum coherence (HSQC) as well as 13C nuclear magnetic resonance (NMR). 1H NMR of rice straw CNCs (4.7 nm thick, 143 nm long, 0.04 sulfate per AG or 19.0% surface hydroxyl to sulfate conversion) resembled that of homogeneous cellulose solution. Conventional 2D HSQC NMR of CNC, CNF 1.5 (2-14 nm thick, several micrometers long, 0.10 COOH per AG) and CNF10 (2.0 nm thick, up to 1 μm long, 0.28 COOH per AG) gave H1:H2 ratios of 1.08:1, 0.97:1 and 0.94:1, respectively, all close to the theoretical 1:1 value for cellulose. The H1:H6 ratios determined from 2D HSQC NMR for CNCs, CNF1.5 and CNF10 were 1:1.47, 1:0.88 and 1:0.14, respectively, and corresponded to 26%, 56% and 93% C6 primary hydroxyl conversion to sulfate and carboxyl groups, consistent with, but more sensitive than those by conductometric titration and X-ray diffraction. Both 1H and 2D HSQC NMR data confirm that solution-state NMR detects nanocellulose surface carbons and protons primarily, validating this technique for direct surface characterization of nanocellulose in aqueous colloidal suspensions, presenting a sensitive and meaningful NMR tool for direct characterizing individual nanocellulose surfaces in never-dried state.

Isoxazolodihydropyridinones: 1,3-Dipolar Cycloaddition of Nitrile Oxides onto 2,4-Dioxopiperidines

Practical and efficient methods have been developed for the diversity-oriented synthesis of isoxazolodihydropyridinones via the 1,3-dipolar cycloaddition of nitrile oxides onto 2,4-dioxopiperidines. A select few of these isoxazolodihydropyridinones were further elaborated with triazoles by copper-catalyzed azide-alkyne cycloaddition reactions. A total of 70 compounds and intermediates were synthesized and analyzed for drug likeness. Sixty-four of these novel compounds were submitted to the NIH Molecular Libraries Small Molecule Repository for high-throughput biological screening.

High-field 1H NMR studies of synthetic analogs of somatostatin: Structural features involving aromatic residues in an active eight-membered ring analog

360 MHz 1H-NMR data are presented for somatostatin and an analog whose primary structure is cyclo(-Gaba-Asn5-Phe6-Phe7-DTrp8-Lys9-Thr10-Phe11-). This report focuses on the aromatic portion of the spectrum, and this region for the analog is unambiguously assigned, using two experimental approaches: selective deuteration and photo-induced CIDNP. The most prominent feature of the analog aromatic spectrum is a two-proton resonance which exhibits a pronounced upfield shift. Significantly, this feature is also present for somatostatin and other active analogs (unpublished data). Assignments show that this resonance derives from the ortho hydrogens of the Phe6 and that aromatic resonances of Phe6 shift markedly upfield as temperature is decreased. In contrast, the aromatic resonances of Phe7,11 and DTrp8 reveal generally much smaller temperature coefficients and shift primarily downfield as temperature is decreased. Ring-current analysis shows that simple pair-wise parallel pi-stacking alone cannot give rise to the observed data. However, a simple hypothesis involving only two phenylalanine residues is totally consistent with the data if they maintain a time-averaged co-perpendicular orientation. Indirect evidence is offered which implicates only one phenylalanine stacking partner for Phe6, which we tentatively identify as Phe11.

2,3-cis-2R,3R-(-)-epiafzelechin-3-O-p-coumarate, a novel flavan-3-ol isolated from Fallopia convolvulus seed, is an estrogen receptor agonist in human cell lines

BackgroundThe plant genus Fallopia is well-known in Chinese traditional medicine and includes many species that contain bioactive compounds, namely phytoestrogens. Consumption of phytoestrogens may be linked to decreased incidence of breast and prostate cancers therefore discovery of novel phytoestrogens and novel sources of phytoestrogens is of interest. Although phytoestrogen content has been analyzed in the rhizomes of various Fallopia sp., seeds of a Fallopia sp. have never been examined for phytoestrogen presence.MethodsAnalytical chemistry techniques were used with guidance from an in vitro estrogen receptor bioassay (a stably transfected human ovarian carcinoma cell line) to isolate and identify estrogenic components from seeds of Fallopia convolvulus. A transiently transfected human breast carcinoma cell line was used to characterize the biological activity of the isolated compounds on estrogen receptors (ER) α and β.ResultsTwo compounds, emodin and the novel flavan-3-ol, (−)-epiafzelechin-3-O-p-coumarate (rhodoeosein), were identified to be responsible for estrogenic activity of F. convolvulus seed extract. Absolute stereochemistry of rhodoeosein was determined by 1 and 2D NMR, optical rotation and circular dichroism. Emodin was identified by HPLC/DAD, LC/MS/MS, and FT/ICR-MS. When characterizing the ER specificity in biological activity of rhodoeosein and emodin, rhodoeosein was able to exhibit a four-fold greater relative estrogenic potency (REP) in breast cells transiently-transfected with ERβ as compared to those transfected with ERα, and emodin exhibited a six-fold greater REP in ERβ-transfected breast cells. Cell type-specific differences were observed with rhodoeosein but not emodin; rhodoeosein produced superinduction of reporter gene activity in the human ovarian cell line (> 400% of maximum estradiol [E2] induction) but not in the breast cell line.ConclusionThis study is the first to characterize the novel flavan-3-ol compound, rhodoeosein, and its ability to induce estrogenic activity in human cell lines. Rhodoeosein and emodin may have potential therapeutic applications as natural products activating ERβ, and further characterization of rhodoeosein is necessary to evaluate its selectivity as a cell type-specific ER agonist.

The isomeric biliverdins from ring-cleavage of deuteroporphyrin-IX

Summary Treatment of zinc(II) deuteroporphyrin-IX dimethyl ester with thallium(III) trifluoroacetate, followed by acid treatment, affords the four isomeric oxophlorins (oxyporphyrins) in a reaction which is considerably more easy to control than the traditional method involving “coupled oxidation” of the corresponding hemin. The oxophlorins, obtained in very high yield, are chromatographically separable on a preparative scale. Using nuclear Overhauser enhancement and NMR spin-decoupling experiments, the isomeric deuterobiliverdins and meso-acetoxyporphyrins derived from the isomerically pure oxophlorins are assigned definitive structures. This work suggests that the original assignments of the β- and δ- deuterobiliverdins, made on the basis of coupled oxidation of deuterohemin-reconstituted hemoglobin, should be reversed. Implications for heme orientation in deuterohemin-reconstituted hemoglobin are discussed.