Steven G. Wood

Solvent, not palladium oxidation state, is the primary determinant for successful coupling of terminal alkynes with iodo-nucleosides☆

Abstract Coupling of iodo-nucleosides with terminal alkynes such as 3-(acylamino)propynes, whose initial products readily undergo secondary cyclization reactions, can be effected smoothly by the standard catalysis with (Ph 3 P) 2 PdCl 2 /CuI/Et 3 N in dimethylformamide.

Hemolysis of erythrocytes and fluorescence polarization changes elicited by peptide toxins, aliphatic alcohols, related glycols and benzylidene derivatives

Hemolysis rates of human erythrocytes induced by C2 and C8-C14 straight chain 1-alkanols, 1,2-alkanediols and the corresponding benzylidene derivatives (benzaldehyde acetals) have been studied and compared with hemolysis rates obtained by three peptide toxins. The peak of activity occurs at C12 for the alkanols and glycols and at C10 for the benzylidene derivatives. The most active compound is 1-dodecanol, followed by 1,2-dodecanediol and the C10 benzylidene acetal, which show 50% hemolysis at 15, 99 and 151 microM, respectively, at 37 degrees C. A few lysolecithins and longer chain cis-unsaturated alcohols were studied for comparison purposes, and were found to be more active than 1-dodecanol. The most active were the 16:0 lysolecithin and cis-9-tetradecene-1-ol, which gave 50% hemolysis at concentrations of 2.8 and 5.6 microM respectively. The hemolytic activities of 1-dodecanol, 1,2-dodecanediol and the C10 benzylidene acetal were compared to activities of Pyrularia thionin and melittin with cow, horse, sheep, pig and human erythrocytes. Whereas the peptide toxins showed clear specificity for human erythrocytes, no selectivity was shown by any of the other compounds tested. Addition of the thionin or Naja naja kaouthia cardiotoxin to erythrocyte ghosts caused a slight but reproducible increase in the order of the phospholipid bilayer, as measured with the fluorescent probe NBD-PC. Cardiotoxin gave a greater response than did the P thionin, and extensively iodinated P thionin gave a smaller change than did P thionin. Similar results were obtained with melittin, but this peptide gave a markedly greater response than all other peptides. Addition of dodecanol or the C10 benzylidene acetal caused a marked increase in membrane fluidity. All of these data indicate that the organic compounds interact directly with and are incorporated nonspecifically into the membrane lipid bilayer, but the peptide toxins interact specifically with some component on the surface of the membrane, either a protein or specific phospholipid domain, followed by insertion into the membrane and decreasing phospholipid movement.

Structure elucidation of compounds extracted from the Chinese medicinal plant Patrinia heterophylla

For several hundred years, Patrinia heterophylla has been used in traditional Chinese medicine as a treatment for abscesses, hepatitis, tonsillitis, ulcers, etc. Recent research suggests that it may also have some anti-cancer activity. We have extracted five pure compounds from this plant; two known flavonols without bio-activity, one known isocoumarin glucoside that exhibits some cytotoxic activity toward HeLa cervical cancer cells, and two novel compounds that show considerable cytotoxic activity toward HeLa cells. Additional Note (Submitted March 2007) In collaboration with: Steven A. Fleming Department of Chemistry and Biochemistry Brigham Young University Provo. Utah. 84602 In the previous paper, compounds A and B were found to be have very similar structures where the only difference lies in one of the side-chains (A = isopropyl and B = propyl). We have further investigated the possible source of the complexity observed in the NMR spectra of these two compounds A and B. The X-ray crystallographic data for the compounds show that both exist in the solid state as one stable structure, whereas in the liquid state it appears that multiple structures exist for both compounds. There are eight possible tautomers for both compounds (figure 1) and the relative energies of the tautomers were calculated using Dewars AM1 semi empirical method. In both instances tautomer 1 (shown encircled) was found to be the most stable. Ab initio calculations using Gausian 98 B3LYP with a 631G basis set carried out on tautomers 1 and 4 (with both side groups replaced by methyl groups) gave O--H bond distances (Å) for the hydrogen bonded segments as shown in figure 2. Upon energy minimization, both tautomers relaxed to the same structure with bond parameters that were in close agreement with those derived from the X-ray data of the most stable structures. Figure 1. Relative Energy of the Tautomers (kcal mol−1). Figure 2. Ab Initio energy calculations and energy minimization of tautomers 1 and 4. If tautomerism were the main cause of the spectral complexity, then decreasing the temperature should result in a preponderance of the most stable form at the expense of the higher energy tautomers, and consequently the NMR spectra should simplify. As described in the main paper the opposite was observed to occur for both compounds A and B. On the other hand, if the spectral complexity was due to rotational isomerism arising from the side-chains, then as the temperature is lowered, so rotation about C--C single bonds becomes more hindered and the possibility increases of stabilizing different conformations with a concomitant increase in spectral complexity. This conclusion is in harmony with the fact that the X-ray data strongly suggests large thermal motion on atoms associated with the side-chains in both compounds.

Synthesis and X-Ray Crystal Structure of 3-Amino-1-β-D-Ribofuranosyl-s-Triazolo[5, 1-c]-s-Triazole

Abstract The first chemical synthesis of 3-amino-1-β-D-ribofuranosyl-s-triazolo[5,1-c]-s-triazole (6) is described. Direct glycosylation of 3-amino-5(7)H-s-triazolo[5,1-c]-s-triazole (2) with 1-O-acetyl-2,3,5-tri-O-benzoyl-D-ribofuranose (3) in the presence of TMS-triflate gave 3-amino-1-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)-s-triazolo[5, 1-c]-s-triazole (4) which, on ammonolysis, gave 6. The absolute structure of 6 is determined by X-ray diffraction techniques employing Mo Kα radiation. The structure is solved by direct methods and refined to the R value of 0.044 by using a full-matrix least-squares method. The sugar of 6 has a 3T2 configuration. The torsion angles about the C5′–C4′ bond are both gauche and the torsion angle about the glycosidic bond is in the anti range. Each azole ring of the aglycon is planar and the dihedral angle between the planes of the rings is 3.6°.

X-ray structure and13C NMR assignments of indole alkaloids fromAspidosperma cruenta

The leaf tissue ofAspidosperma cruenta was studied for alkaloid content. Two alkaloids were isolated and shown by a combination of MS, X-ray, and high field NMR analysis to be obscurinervine and obscurinervidine. X-ray analysis of obscurinervine provided the first quantitative structural information on this compound. Obscurinervine (C25H30N2O5) crystallized in the monoclinic space groupP21 with unit cell parametersa=12.863(3)Å,b=9.646(2)Å,c=18.484(3)Å,β=105.14(5)°,V=2213.8(8)Å3,Dc=1.316 Mg/m3, andZ=4. The structure was solved by direct methods and refined toR=0.054 for 3468 observed reflections. The 2D INADEQUATE NMR experiment provided the first13C chemical shift assignments for obscurinervine. Nineteen of the 2313C-13C connections present were detected. Corresponding13C assignments for obscurinervidine were made by comparison to the spectrum of obscurinervine. The average natural concentrations of the alkaloids were determined to be 0.780% (obscurinervine) and 0.737% (obscurinervidine) by HPLC analysis. Obscurinervine was tested for antiviral and cytotoxic effects. Noin vitro activity was observed.

NMR characterization of obscurinervine and obscurinervidine using novel computerized analysis techniques

The 13C and 1H resonances of the alkaloids, obscurinervine (1) and obscurinervidine (2), are assigned using high-field NMR experiments and computerized data analysis procedures. A 2D INADEQUATE analysis of 26 mg of 2 was performed with a high-sensitivity carbon probe and the data interpreted using the spectral analysis program, CCBOND, to provide unambiguous 13C assignments. Although all signals are visually undetectable, CCBOND determined 20 of the 22 carbon–carbon bonds present. Corresponding 1H chemical shift assignments are made from HETCOR data. Proton–proton couplings are determined from DQF-COSY data using the new analysis program, HHCORR. Since HHCORR models signals as AB spin systems, the determined coupling constants are fairly independent of higher order effects, linewidths and digital resolution. Also a significant sensitivity improvement over visual interpretation of DQF-COSY data is observed. The obtained coupling constants are interpreted through the Karplus relationship to provide conformational details. These novel software analysis techniques allow accurate and more routine analysis of INADEQUATE and DQF-COSY data providing non-specialists access to these powerful experiments. Absolute stereochemistry of 2 is determined by a comparison with the ORD curve of(–)-O-methylaspidolimine. Stereospecific 1H assignments are obtained from proton–proton couplings and molecular mechanics simulations. The 13C and 1H chemical shift assignments for the related alkaloid, obscurinervine 1, are determined from CCBOND processed 2D INADEQUATE, HHCORR processed DQF-COSY, and HETCOR data. Differences in the rigidity of 1 and 2 in dimethyl sulfoxide (DMSO) are quantified by variable-temperature 1H NMR spectroscopy. Complete conformations of all ring systems are obtained from molecular mechanics using dihedral angles derived from proton–proton couplings as a check on the quality of the model. All conformational conclusions are independently supported by the X-ray structure of 1.

The Role of Glycosylases in Mismatch Repair: The Use of 7-Deazapurines as Repair-Resistant Lesions in Oligonucl, Eotide-Directed Mutagenesis

Abstract The mechanism of mismatch repair from phclqe DNA was studied using the techniques of oligonucleotide-directed mutagenesis. 7-kazaanalogues of deoxy-adenosine and deoxy-inosine were found to be excised with impaired repair efficiency following transfection into E.coli JM101.

The Synthesis and Base-Pairing Properties of 2-Deoxy-7-deazanebularine

Abstract 2-Deoxy-7-deazanebularine-5-triphosphate (dDNTP) was used as a substrate for DNA polymerase. It was found to be an effective substitute for dATP, but not for dGTP, under standard conditions of in vitro primer extension reactions.