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K H Schram

Publications and source records attributed to K H Schram.

At least 19 recordsLinked to original sources
PubMed2000

Design and synthesis of conformationally constrained glucagon analogues.

Glucagon was systematically modified by forming lactam bridges within the central region of the molecule to give conformationally constrained cyclic analogues. Six cyclic glucagon analogues have been designed and synthesized. They are c[Asp(9),Lys(12)][Lys(17,18), Glu(21)]glucagon-NH(2) (1), c[Asp(9),Lys(12)]glucagon-NH(2) (2), c[Lys(12),Asp(15)]glucagon-NH(2) (3), c[Asp(15), Lys(18)]glucagon-NH(2) (4), [Lys(17)-c[Lys(18), Glu(21)]glucagon-NH(2) (5), and c[Lys(12),Asp(21)]glucagon-NH(2) (6). The receptor binding potencies and receptor second messenger activities were determined by radio-receptor binding assays and adenylate cyclase assays, respectively, using rat liver plasma membranes. Most interestingly, analogues 1, 2, 3, and 4 were antagonists of glucagon stimulated adenylate cyclase activity, whereas analogues 5 and 6 were partial agonists in the functional assay. All of the cyclic analogues were found to have reduced binding potencies relative to glucagon. The structural features that might be responsible for these effects were studied using circular dichroism spectroscopy and molecular modeling. These results demonstrated the significant modulations of both receptor binding affinity and transduction (adenylate cyclase activity) that can accompany regional conformational constraints even in larger polypeptide ligands. These studies suggest that the entire molecular conformation, including the flexible middle portion, is important for molecular recognition and transduction at the hepatic glucagon receptor.

Amino Acid Sequence↗
PubMed2000

Tandem mass spectrometry studies of green tea catechins. Identification of three minor components in the polyphenolic extract of green tea.

Liquid chromatography/electrospray ionization mass and tandem mass spectrometry (MS/MS) techniques were used to identify two minor components and one new compound in the polyphenolic extract of green tea (Camellia sinensis). Identification and structure assignments were based on previously reported sub-structural features in the MS/MS product, precursor and neutral loss scans of reference samples. The structures of two minor components, related to the known green tea components epicatechin gallate (ECG, 5) and epigallocatechin gallate (EGCG, 6), are formed by methylation at the 3"-O-position of the gallic acid moiety. The new compound contained a gallic acid ester group, but had only one phenolic group in either the A- or B-ring, relative to the structure of 5. High-resolution mass measurements supported the empirical formula assigned to the new compounds. An important fragmentation for defining the position of methylation of the ester function involves ionization of the phenolic group at the 4"-position of the gallic acid, followed by elimination of the ester function as a neutral with concomitant formation of the m/z 169 ion. If the 4"-position is blocked by methylation, the formation of m/z 169 incorporating the gallic acid group would be blocked. Thus, the presence of an ion representing the ester group indicates a free 4"-phenol and the absence of this ion would signify the 4"-position as a site of methylation. The operation of this mechanism should be general and useful in assigning the site of methylation of any polyphenolic ester group in natural products. A similar conclusion can be drawn concerning alkylation or esterification of the 4'-position of the catechins, i. e. blocking the 4'-phenol would prevent formation of the m/z 125 ion common to all of the catechin compounds thus far examined. Therefore, mass spectral data are of considerable importance in deducing the sites of alkylation or esterification in the structures of the components of green tea.

Catechin↗
PubMed1998

Mass spectrometry of selected components of biological interest in green tea extracts.

Mass spectrometric methods including EIMS, FABMS, and LC/ESIMS have been surveyed as tools for the detection of catechins in extracts of green tea (Camellia sinensis). EIMS provide both molecular weight and structure information, including epimer differentiation, on compounds 1, 2, and 4 and some structural information with compounds 5 and 6. FABMS gives both molecular weight and structure information, by an retro-Diels-Alder mechanism, on all compounds. LC/ESIMS provides unambiguous molecular weight information on all compounds and some additional structural data are evident in the mass spectra of 5 and 6. LC/ESIMS is, thus, shown to be an appropriate method for the direct analysis of crude extracts of green tea. The information obtained in this work will be of importance in future studies involving identification of the components of green tea and for characterization of synthetic analogues.

Catechin↗
PubMed1997

Mass spectrometry of nucleotides and oligonucleotides.

Recent advances in the use of mass spectrometry for the determination of the molecular weight and sequencing of oligonucleotides are discussed. Matrix-assisted laser desorption (MALDI) and electrospray ionization (ESI) mass spectrometry have been shown to be especially important techniques for both molecular weight assignment and sequencing of oligonucleotides, and are the focus of this article which covers the literature through early 1996.

Humans↗
PubMed1997

Isolation of isoflavones from soy-based fermentations of the erythromycin-producing bacterium Saccharopolyspora erythraea.

A search for an abundant and economical source of isoflavones, particularly genistein, led to the discovery that the erythromycin-producing organism Saccharopolyspora erythraea also produces this promising new cancer-prevention agent. Erythromycin fermentation is a large-scale, soybean-based process used world-wide for the commercial production of this medically important antibiotic. Results from this study indicate that genistin (the glucoside form of genistein), which is added to the fermentation in the soybean media, was converted to genistein through the action of a beta-glucosidase produced by the organism. Genistein was co-extracted with erythromycin from the fermentation broth, then separated from erythromycin during the second step of the purification process for the production of erythromycin.

Chromatography, High Pressure Liquid↗
PubMed1995

Evaluation of mass spectrometric techniques for characterization of engineered proteins.

Mass spectrometric characterization of engineered proteins has been examined using bovine recombinant Acyl-CoA-Binding Protein (rACBP), [15N]-labeled rACBP, and a number of sequence variants of ACBP produced by site-directed mutagenesis. The mass spectrometric techniques include ESIMS and MALDIMS for analysis of the intact protein. Peptide maps have been obtained either by direct analysis of enzymatically derived mixtures by PDMS, ESIMS, and MALDIMS or by off- and on-line HPLC-mass spectrometry. ESIMS was found to be most accurate for analysis of intact proteins. The best sequence coverage in mapping was obtained by LC-ESIMS and by direct mixture analysis by MALDIMS. The latter technique was favorable in terms of sensitivity and speed. A general strategy for mass spectrometric characterization of engineered proteins is suggested.

Amino Acid Sequence↗
PubMed1993

Synthesis of thiazole-4-carboxamide-adenine difluoromethylenediphosphonates substituted with fluorine at C-2' of the adenosine.

Synthesis of an analogue 3 of thiazole-4-carboxamide adenine-dinucleotide (TAD) in which the beta-oxygen atom of the pyrophosphate bridge is replaced by a difluoromethylene group has been achieved. Likewise, 2'-deoxy-2'-fluoroadenosine containing analogues of TAD (4) and its difluoromethylenediphosphonate congener (5) have been synthesized. Adenosine 5'-difluoromethylenediphosphonate (8) was prepared from 5'-O-tosyladenosine (6) and tris(tetra-n-butylammonium)difluoromethylenediphosphonate (7) by a modified procedure of Poulter's. Compound 8 was converted into the 2',3'-cyclic carbonate 9 by treatment with triethyl orthoformate. Treatment of 9 with 2',3'-O-isopropylidenetiazofurin (10) in pyridine in the presence of DCC gave a mixture of dinucleotide 11 and the isopropylidene-protected diadenosine tetraphosphonate 12. After deprotection of 11, the desired beta-difluoromethylene TAD (3) was separated by HPLC as the minor product. The diadenosine tetraphosphonate 12, an analogue of Ap4A, was obtained as the major component. Alternatively, 2',3'-O-isopropylidenetiazofurin (10) was tosylated, and the product 13 was further converted into the corresponding difluoromethylenediphosphonate 14 by coupling with 7. DCC-catalyzed coupling of 14 with 2'-deoxy-2'-fluoroadenosine (15) followed by deisopropylidenation afforded the analogue 5. Again the corresponding tetraphosphonate analogue of tiazofurin 17 was the predominant product. Dinucleotide 4 was obtained by coupling of the carbonyldiimidazole-activated tiazofurin 5'-monophosphate with 2'-deoxy-2'-fluoroadenosine 5'-monophosphate. 2'-Deoxy-2'-fluoroadenosine (15) was prepared efficiently from the known N6-benzoyl-3'-O-tetrahydropyranyladenosine (18), which was converted into 3'-O-tetrahydropyranyl-2'-O-triflyl-5'-O-trityladenosine (20) by tritylation and triflation. Treatment of 20 with sodium acetate in hexamethylphosphoric triamide, followed by deacetylation afforded 9-(3-O-tetrahydropyranyl-5-O-trityl-beta-D- arabinofuranosyl)-N6-benzoyladenine (22), which was then treated with DAST. After deprotection of the product, 15 was obtained in good yield.

Adenine Nucleotides↗
PubMed1993

Urinary excretion of modified nucleosides as biological marker of RNA turnover in patients with cancer and AIDS.

Using boronate gel affinity chromatography and reversed-phase high-performance liquid chromatography (RP-HPLC), a method for the simultaneous determination of 12 urinary modified nucleosides has been developed. The RP-HPLC fractions were identified by gas chromatography/mass spectrometry analysis. The HPLC quantitation of urinary nucleoside levels before and after surgery of cancer patients suggested that urinary 5'-deoxy-5'-methylthioadenosine and N-[(9-beta-D-ribofuranosyl-9H-purine-6-yl) carbamoyl]-L-threonine (t6A) levels were helpful in monitoring therapeutic effects in cancer patients. From the fact that molar ratios of urinary N2,N2-dimethylguanosine (m2 2G)pseudouridine (psi) and t6A/psi in cancer patients were lower than those of normal or post-surgical cancer patients, the increase of rRNA content in cancer tissues growing rapidly was estimated using the stoichiometric relationship between the ratio of the number of residues of their modified nucleoside in RNAs and the proportion of rRNA to total RNAs in average tissues of whole body. Furthermore, from the estimation of RNA turnover using urinary nucleoside levels, it was found that the half-lives of rRNA rather than tRNA of patients with cancer and those of both RNAs in the case of acquired immunodeficiency syndrome (AIDS) were extremely short compared with those of the normal. Thus, we discovered that the selected urinary modified nucleosides were very useful as a biological marker of whole-body RNA turnover in patients with cancer and AIDS.

Acquired Immunodeficiency Syndrome↗
PubMed1993

Characterization of linear and cyclic glucagon analogs by fast atom bombardment mass spectrometry.

Fast atom bombardment mass spectral mapping of endoproteinase Asp-N digest mixtures is used for characterization of new synthetic linear and cyclic glucagon analogs. The results allow rapid identification of sequence modifications in linear glucagon analogs. For the cyclic compounds, the technique allows confirmation of the presence and position of the cyclic amide bond, as well as verification of the sequence of the modified glucagon analogs. The specificity of the Asp-N enables differentiation of isometric glucagon analogs which differ only in the position of the cyclic amide bond. Important information concerning the purity of the synthetic analogs is also available.

Amino Acid Sequence↗
PubMed1993

Gas chromatography/mass spectrometric analysis of urinary nucleosides in cancer patients; potential of modified nucleosides as tumour markers.

Analysis of urine from cancer patients by capillary gas chromatography/mass spectrometry positively identified 14 urinary nucleosides including several modified nucleosides. Levels of the modified nucleosides 1-methyl-adenosine, 2-methylguanosine, N2,N2-dimethylguanosine and 1-methylinosine as well as the total nucleoside level were elevated in the urine when a malignant tumour was present; the levels of N2,N2-dimethylguanosine were found to correlate with the stage of the cancer.

Adenosine↗
PubMed1991

Estimation of whole-body RNA catabolism based on the urinary modified nucleoside levels of cancer and AIDS patients.

From the relationship between the molar ratio of nucleosides calculated stoichiometrically from modified nucleoside occurrences in major RNA species and the proportion of rRNA to all of RNA contents in average tissues, the increase of rRNA contents in cancer tissues growing rapidly was found. Thus, we found that selected urinary modified nucleoside levels were very useful as a biological marker of cancer and AIDS, as well as a good indicator of whole-body metabolic conditions of RNAs.

Acquired Immunodeficiency Syndrome↗
PubMed1990

Isolation and identification of urinary nucleosides. Applications of high-performance liquid chromatographic methods to the synthesis of 5'-deoxyxanthosine and the simultaneous determination of 5,6-dihydrouridine and pseudouridine.

Modified nucleosides from pooled normal human urine were extracted using a boronate affinity gel column and fractionated by reversed-phase high-performance liquid chromatography (RP-HPLC). The major constituents in each of the 30 RP-HPLC fractions were determined by gas chromatography-mass spectrometry of the trimethylsilyl derivatives of the fractions. The same RP-HPLC method was used in the synthesis of 5'-deoxyxanthosine from authentic 5'-deoxyadenosine. In addition, the simultaneous determination of urinary 5,6-dihydrouridine (D) and pseudouridine (psi) was carried out by RP-HPLC using two ODS columns in series. The level of D in pooled normal urine was 4.87 nmol/mumols creatinine. The RP-HPLC method was applied to the measurement of D and psi levels in urines collected before and after surgery from four patients with gastrointestinal cancer. A large decline in both nucleoside levels in urines after surgery was observed in three of the four cancer patients.

Chromatography, High Pressure Liquid↗
PubMed1990

Analysis, identification and determination of urinary modified nucleosides of cancer and AIDS patients.

Modified nucleoside levels in urine samples collected before and after surgery from seven patients with malignant gastrointestinal cancer were examined by the reversed-phase HPLC method. Those of an AIDS patient, a breast cancer patient, and pooled normal urines were also compared. To monitor the effects of therapy on cancer patients, the levels of modified nucleosides, especially t6A and MTA, were found to be fairly effective. In an AIDS patient, the levels of most of the nucleosides exhibited remarkable increases compared to normal urine.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Differentiation of isomeric 2'-, 3'- and 5'-deoxynucleosides by electron ionization and chemical ionization-linked scanning mass spectrometry.

A comparative mass spectral examination of the trimethylsilyl (TMS) derivatives of 2'-, 3'- and 5'-deoxyadenosine, 2'-, 3'- and 5'-deoxyguanosine, 2'-, 3'- and 5'-deoxyxanothosine and 2'- and 5'-deoxy-2-fluoroadenosine is presented. A general compilation of the major fragment ions found in the low-resolution electron ionization (EI) spectra of the eleven deoxynucleosides is given. Chemical ionization (CI)-collisional activation (CA) daughter ion spectra are reported using the deoxyadenosines as model compounds. Ion structures and fragmentation pathways are proposed for those ions characteristic of each of the isomers. Significant differences in fragmentation exist between the isomeric 2'-, 3'- and 5'-purine deoxynucleosides. The formation and structures of ten ions important in this differentiation are discussed. The CI-CA linked scan spectra provide complementary structural information relative to the EI mass spectra.

Deoxyribonucleosides↗
PubMed1989

Deuterium-labeled 3-nitrobenzyl alcohol as a matrix for fast atom bombardment mass spectrometry.

The utility of deuterium-labeled 3-nitrobenzyl alcohol (DNBA) as a fast atom bombardment (FAB) matrix for establishing the number of exchangeable hydrogens present in a molecule is illustrated by the analysis of five selected antitumor agents. A method for the simple preparation of this labeled matrix is described. The use of DNBA may be of value for samples which provide no FAB spectra when deuterium-labeled glycerol is used as a matrix.

Benzyl Alcohols↗