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H L Carrell

Publications and source records attributed to H L Carrell.

At least 19 recordsLinked to original sources
PubMed1992

Molecular conformation of estramustine and two analogues.

The crystal and molecular structures of estramustine and two of its analogues have been determined by X-ray crystallographic techniques (a total of three different compounds). The compounds studied are estramustine [1,3,5(10)-estratriene-3,17 beta-diol-3-N,N-bis(2'- chloroethyl)carbamate] and its monohydrate, estromustine [17-oxo-1,3,5(10)-estratriene-3-yl-N,N-bis(2'-chloroethyl)carbamate], and 17-oxo-5-androsten-3 beta-yl-N,N-bis(2'-chloroethyl)carbamate. Three views of estramustine were obtained from the study of its two crystal forms. The main structural features found are as follows: (a) the geometries of the steroid moieties are closely similar to those of the parent steroids, (b) the bonds around the nitrogen atom of the nitrogen mustard grouping lie approximately in a plane in each structure, (c) the plane through the carbon atoms of the steroid A-ring lies approximately perpendicular to the plane through the carbamate atoms in each structure, (d) the carbonyl C-O of the carbamate points to the alpha side of the steroid moiety in each structure, and (e) one chlorine atom of the nitrogen mustard grouping makes a close contact [3.13 A], in each structure, to the nitrogen atom. Hydrogen bonding to the carbamate appears to occur from the alpha side of the steroid; there is no hydrogen bonding to the nitrogen atom of the carbamate group. These structural data provide some steric explanations for the resistance of the carbamate to enzymatic hydrolysis. The long in vivo half-life of the intact estramustine molecule is a result of this stability. This is responsible for the absence of alkylating ability and the propensity of the drug to bind microtubule-associated proteins and express an antimitotic mechanism of action.

Estramustine↗
PubMed1991

The crystal and molecular structure of ellagic acid dihydrate: a dietary anti-cancer agent.

The crystal and molecular structure of ellagic acid dihydrate has been determined by X-ray diffraction techniques. This acid inhibits the carcinogenic properties of a variety of chemical compounds including benzo[alpha]pyrene-7,8-diol-9,10-epoxide, aflatoxin B1, N-methyl-N-nitrosourea, 3-methyl-cholanthrene and 7,12-dimethylbenz[alpha]anthracene. Ellagic acid dihydrate forms triclinic crystals with unit cell dimensions: a = 7.656(1) A, b = 9.563(1)A, c = 4.623(1) A, alpha = 97.88(1) degrees, beta = 103.2(1) degrees, gamma = 102.22(1) degrees, V = 315.9 A3, space group = P1. There is a center of symmetry in the crystal coinciding with the center of the molecule, so that there is only one molecule in the unit cell. Ellagic acid is planar and molecules are interconnected by hydrogen bonds to water, giving rise to layers of molecules throughout the crystal. Its activity and anti-cancer properties are compared with those of a similar naturally occurring compound, quercetin.

Antineoplastic Agents↗
PubMed1989

X-ray analysis of D-xylose isomerase at 1.9 A: native enzyme in complex with substrate and with a mechanism-designed inactivator.

The structures of crystalline D-xylose isomerase (D-xylose ketol-isomerase; EC 5.3.1.5) from Streptomyces rubiginosus and of its complexes with substrate and with an active-site-directed inhibitor have been determined by x-ray diffraction techniques and refined to 1.9-A resolution. This study identifies the active site, as well as two metal-binding sites. The metal ions are important in maintaining the structure of the active-site region and one of them binds C3-O and C5-O of the substrate forming a six-membered ring. This study has revealed a very close contact between histidine and C1 of a substrate, suggesting that this is the active-site base that abstracts a proton from substrate. The mechanism-based inhibitor is a substrate analog and is turned over by the enzyme to give a product that alkylates this same histidine, reinforcing our interpretation. The changes in structure of the native enzyme, the enzyme with bound substrate, and the alkylated enzyme indicate that the mechanism involves an "open-chain" conformation of substrate and that the intermediate in the isomerization reaction is probably a cis-ene diol because the active-site histidine is correctly placed to abstract a proton from C1 or C2 of the substrate. A water molecule binds to C1O and C2O of the substrate and so may act as a proton donor or acceptor in the enolization of a ring-opened substrate.

Aldose-Ketose Isomerases↗
PubMed1987

Metabolism of 19-methyl-substituted steroids by human placental aromatase.

The 19-methyl analogues of androstenedione and its aromatization intermediates (19-hydroxyandrostenedione and 19-oxoandrostenedione) were evaluated as substrates of microsomal aromatase in order to determine the effect of a 19-alkyl substituent on the enzyme's regiospecificity. Neither the androstenedione analogue [10-ethylestr-4-ene-3,17-dione (1c)] nor the 19-oxoandrostenedione analogue [10-acetylestr-4-ene-3,17-dione (3c)] was converted to estrogens or oxygenated metabolites by placental microsomes. In contrast, both analogues of 19-hydroxyandrostenedione [10-[(1S)-1-hydroxyethyl]estr-4-ene-3,17-dione (2c) and 10-[(1R)-1-hydroxyethyl]estr-4-ene-3,17-dione (2e)] were converted to the intermediate analogue 3c in a process requiring O2 and either NADH or NADPH. No change in enzyme regiospecificity was detected. The absolute configuration of 2e was determined by X-ray crystallography. Experiments with 18O2 established that 3c generated from 2c retained little 18O (less than 3%), while 3c arising from 2e retained a significant amount of 18O (approximately equal to 70%). All four 19-methyl steroids elicited type I difference spectra from placental microsomes in addition to acting as competitive inhibitors of aromatase (KI = 81 nM, 11 microM, 9.9 microM, and 150 nM for 1c, 2c, 2e, and 3c, respectively). Pretreatment of microsomes with 4-hydroxyandrostenedione (a suicide inactivator of aromatase) abolished the metabolism of 2c and 2e to 3c, as well as the type I difference spectrum elicited by 2c and 2e.(ABSTRACT TRUNCATED AT 250 WORDS)

Aromatase↗
PubMed1987

Comparison of backbone structures of glucose isomerase from Streptomyces and Arthrobacter.

The C alpha backbones of the glucose isomerase molecules of Streptomyces rubiginosus and Arthrobacter have been determined by X-ray crystallography and compared. Each molecule is a tetramer of eight-stranded alpha/beta barrels, and the mode of association of the tetramers is identical in each case. The Arthrobacter electron density shows four additional amino acids at the carboxyl terminus. There is also an insertion of six amino acids at position 277, and two individual insertions at about positions 348 and 357 (numbering according to the Streptomyces structure). There is a close structural homology throughout the whole molecule, which is most accurate up to position 325. The r.m.s. displacement for 315 homologous C alpha positions up to this position is 0.92 A.

Aldose-Ketose Isomerases↗
PubMed1977

Structure of a dinucleoside phosphate--drug complex as model for nucleic acid--drug interaction.

The crystal structure of a 3:2 complex of the frameshift mutagen proflavine with the dinucleoside phosphate cytidylyl-3'5'-guanosine has been determined. The complex has one drug molecule intercalated between Watson--Crick base pairs of the nucleotide duplex. The other two proflavine molecules are bound to the exterior of the miniature double helix. The orientation of the base pairs in this miniature double helix has aspects similar to that found in RNA 11.

Acridines↗
PubMed1976

Alpha-S-cysteinylthymine: a model for protein-nucleic acid cross-linking.

Crystals of alpha-S-cysteinylthymine, C8H12CIN3O4S, formula weight 281.72, are orthorhombic, space group P212121, with a=9.499 (1), b=24.072 (4), and c=5.012 (1) A, V=1146.1 (2) A3, and Z=4. The structure was determined by the direct method and refined by a full-matrix least-squares procedure to a final residual, R=0.043, using 1277 diffractometer data. From the structure, a three-dimensional model for the radiation-induced interaction of thymine residues and cysteine residues could be postulated.

Binding Sites↗
PubMed1976

Aggregation of acridine orange: crystal structure of acridine orange tetrachlorozincate 2C17H19N3-2HCl-ZnCl2-CH3COOH.

The crystal structure of the biological stain, "acridine orange," has been determined. This compound, when crystallized from ethanol, is shown to be a zinc chloride double salt of acridine orange, containing, in addition, acetic acid of crystallization. These additional components are residuals from the method of preparation of acridine orange. This complex, 2 acridine orange-2HCl-ZnCl2-CH3COOH, (2C17H19N3-2HCl-ZnCl2-CH3COOH) crystallizes in the monoclinic space group P21, a = 9.965 (2), b = 21.507 (6), c = 9.645 (2) A, beta = 113.98 degrees (2), V = 1888.7 (8) A3, FW = 800.0, Z = 2, DX = 1.41 g-cm-3, Dobs = 1.43 (9) g-cm-3. Three-dimensional diffraction data were collected with CuKalpha radiation, and the structure refined to R = 0.065 for 1885 observed reflections. In the crystal structure hydrogen bonds are formed, via the protonated nitrogen atom of the central rings of two acridine orange cations, to two chloride ions in a ZnCl42- tetrahedral grouping. These two acridine orange molecules are stacked in parallel planes, approximately 3.4 A apart, with the long axes of the ring systems inclined at 26.5 to each other. Thus an apparent dimerization of the acridine, orange is facilitated by the anions present, resulting in the complex studied. The two -N(CH3)2 groups of each acridine orange molecule are not protonated in this crystalline form. The mode of molecular packing found here may be relevant to models for the external stacking of acridine orange around a DNA molecule. The importance of removing any zinc salt from acridine orange preparations prior to aggregation studies is stressed.

Acridines↗
PubMed1976

Molecular structures of the chemical carcinogens 7-chloromethylbenz(a)anthracene and 7-chloromethyl-12-methylbenz(a)anthracene.

The three-dimensional structures of two carcinogens, 7-chloromethyl-12-methylbenz[a]anthracene and 7-chloromethylbenz[ai1anthracene, have been determined by X-ray crystallographic techniques. Both compounds are carcinogenic and are believed to act by alkylating DNA. However, the first has a nonplanar ring system, whereas the second has a planar ring system. The nonplanarity of 7-chloromethyl-12-methylbenz[a]anthracene results from steric hindrance between a hydrogen atom of the 12-methyl group and a hydrogen atom on the [a] ring. This molecule cannot be made planar unless the 12-methyl group or the [a] ring is removed. It is concluded that the carcinogenic activity of these compounds does not correlate with planarity of the ring system. This implies that, if DNA is the critical target of attack by these carcinogens, complete intercalation of the aromatic ring system of the carcinogen between the bases of DNA is not a likely mechanism of carcinogenic action in this system of compounds. The results presented here and those of others are more consistent with a model for a common interaction of the carcinogens 7-chloromethyl-12-methylbenz[a]anthracene and 7-chloromethylbenz[a]anthracene with DNA, in which they alkylate the bases of DNA and then lie with their long axes approximately parallel to the helix axis, probably in the major groove.

Alkylation↗
PubMed1976

Molecular structure of benzo(a)pyrene 4,5-oxide.

An X-ray crystallographic study of benzo(a)pyrene 4,5-oxide, a metabolite of the carcinogen benzo(a)pyrene (BP), as given information on the geometry of this molecule. The carbon skeleton of BP itself has been shown by others to be early planar; the planarity of the carbon skeleton has been shown by this work to be perturbed very little by epoxidation of the 4,5-double bond. Epoxidation has, however, increased the double bond character of C-11--C-12, C-9--C-10, and C-7--C-8. The hydrogen atom on C-3 points directly toward the oxygen atom of another molecule. This C--H... O interaction, although weak, suggests that C-3 might be slightly acidic. An analysis of the experimentally determined bond lengths indicates that, after the highly reactive epoxide ring, the most reactive positions are at C-1, C-6, C-7, C-11, and C-12. The oxide ring of BP, unlike that for the K-region oxide of 7,12-dimethylbenz(a)anthracene, is symmetrical (with C--O distances equivalent within experimental error). The C--O distances are longer than those found in most oxides, including those in 7,12-dimethylbenz(a)anthracene-5,6-oxide. Thus it has been shown that the oxide rings of the K-region oxides of the two potent carcinogens BP and 7,12-dimethylbenz(a)anthracene are not similar in dimensions.

Benzopyrenes↗