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Biomedical subjects

O Buchardt

Publications and source records attributed to O Buchardt.

At least 37 records · Page 2Linked to original sources
PubMed1993

Peptide amidation by enzymatic transacylation and photolysis.

A series of model peptides with a C-terminal protected amide group were prepared by enzymatic transacylation. The protection groups were removed by photolysis to give the warranted peptide amides in high yields. Furthermore, fragments of human calcitonin were prepared. Various protective groups were employed, and the pH, solvent and concentration dependency of the enzymatic transcylation were examined. The photo-cleavage reaction was examined for wavelength, concentration and pH dependency. It was shown that the optimal yields required addition of a chemical scavenger for the photolysis byproducts.

Acylation↗
PubMed1993

New compounds related to podophyllotoxin and congeners: synthesis, structure elucidation and biological testing.

4-Azido, 4-amino, 4-amido and 4-alkoxy compounds related to the lignans podophyllotoxin and 4'-demethylepipodophyllotoxin have been synthesized, and their structures elucidated. The Ritter reaction was shown to be useful in the preparation of the 4-amido compounds with the required stereochemistry. A preparative method for 4-chloro-4-deoxypicrophyllotoxin, for which all earlier synthetic attempts resulted in the two dehydrated compounds, alpha- and beta-apopicropodophyllotoxin, was developed. Supplementary preliminary studies of the biological activities of some of the compounds were performed. All compounds had pronounced inhibitory effect on the in vitro growth of human cervical cancer cells and TC-mouse cells with 4-amino-4-deoxypodophyllotoxin and 4-azido-4-deoxypodophyllotoxin showing the highest activity. Alkaline elution studies indicate that the toxicity of the 4'-demethoxy derivatives is due to protein-mediated DNA nicking. None of the compounds were found to have antiviral effect against herpes simplex type 2 (HSV-2), human immunodeficiency (HIV), and cytomegalovirus (CMV) in doses not toxic to the cells.

Animals↗
PubMed1993

Peptide nucleic acids (PNAs): potential antisense and anti-gene agents.

The binding of peptide nucleic acids (PNAs) T10-LysNH2, T5CT4-LysNH2 and T2CT2CT4-LysNH2 to double-stranded DNA targets A10, A5GA4 and A2GA2GA4 was studied by nuclease S1 probing. It is found that the PNAs bind preferentially to their complementary targets, weaker to targets containing one mismatch and not to targets containing two mismatches. Using an RNA polymerase T3 in vitro transcription system, it is found that a PNA T10-LysNH2 bound downstream from the promoter causes transcription elongation arrest at the PNA binding site only when the PNA is bound to the template strand. Finally, it is shown that primer extension by Taq DNA polymerase on a single-stranded template is arrested at an occupied PNA T10 binding site. These results are discussed in relation to PNAs as potential anti-sense and anti-gene drugs.

Base Sequence↗
PubMed1991

Sequence-selective recognition of DNA by strand displacement with a thymine-substituted polyamide.

A polyamide nucleic acid (PNA) was designed by detaching the deoxyribose phosphate backbone of DNA in a computer model and replacing it with an achiral polyamide backbone. On the basis of this model, oligomers consisting of thymine-linked aminoethylglycyl units were prepared. These oligomers recognize their complementary target in double-stranded DNA by strand displacement. The displacement is made possible by the extraordinarily high stability of the PNA-DNA hybrids. The results show that the backbone of DNA can be replaced by a polyamide, with the resulting oligomer retaining base-specific hybridization.

Base Sequence↗
PubMed1991

Photochemistry of quinolylmethylisothioronium salts. Guanine selective DNA photocleavage reagents.

Quinolylmethylisothioronium salts (1a and 4a) cleave DNA upon irradiation. The cleavage is more than 10-fold enhanced by piperidine treatment and subsequently shows a high preference for guanines. Photolysis of 1a, 2a and 4a in water at lambda greater than 300 nm resulted in photoheterolysis. Irradiation of 1a in 2-propanol gave only products from photohomolysis, irradiation of 1a in methanol and 2a and 4a in 2-propanol resulted in products from both photoheterolysis and photohomolysis. Quantum yields for the disappearance of 1a in water and 2-propanol were determined. The presence or absence of oxygen had no effect in water, whereas oxidation products were observed upon irradiation in methanol and 2-propanol in the presence of oxygen. The guanine specific DNA photoreaction is proposed to take place by alkylation at N7 via the quinolylmethyl carbocation and thus to represent a photoalkylation.

Base Sequence↗
PubMed1988

Photochemical cleavage of DNA by nitrobenzamides linked to 9-aminoacridine.

Nitrobenzamido ligands linked to the DNA intercalator 9-aminoacridine via poly(methylene) chains induce single-strand nicks in DNA upon irradiation with long-wavelength ultraviolet light (lambda greater than or equal to 300 nm). Optimal photocleavage activity was found for the reagent 9-[[6-(4-nitrobenzamido)hexyl]amino]-acridine. Removal of the acridinyl ligand or changing the position of the nitro group from the 4- to the 2-position caused a 10-fold decrease in photocleavage efficiency, whereas a change to the 3-position caused a 30-fold reduction. The DNA cleavage was 5-fold enhanced by subsequent piperidine treatment and showed some sequence dependency with predominant cleavage at G and T residues. Furthermore, significant differences in cleavage preference were observed when the poly(methylene) linker length was changed.

Aminoacridines↗
PubMed1988

Uranyl salts as photochemical agents for cleavage of DNA and probing of protein-DNA contacts.

Single-strand DNA nicks are induced by uranyl nitrate or uranyl acetate in combination with long-wavelength (lambda approximately 420 nm) ultraviolet irradiation. The nicks occur randomly with respect to the DNA sequence. Using the lambda-repressor/ORI operator DNA system it is shown that uranyl salts can be used to photofootprint protein contacts with the DNA backbone.

Bacteriophage lambda↗
PubMed1988

Photocleavage of DNA and photofootprinting of E. coli RNA polymerase bound to promoter DNA by azido-9-acridinylamines.

The long-wavelength ultraviolet (lambda approximately 420 nm) radiation induced reaction between 6-azido-2-methoxy-9-acridinylamines and supercoiled plasmid DNA results in single strand scissions and formation of covalent adducts (ratio approximately 1:10). By treating azidoacridine-photomodified DNA with piperidine at 90 degrees C, additional strand scissions are observed in a complex sequence dependent manner with an overall preference for T greater than or equal to G greater than C much greater than A. The resulting DNA fragments migrate as 5'-phosphates in polyacrylamide gels. Photofootprinting of the binding site of RNA-polymerase on promoter DNA is demonstrated with an azido-9-acridinylamino-octamethylene-9-aminoacridine. Similar experiments using 9-amino-6-azido-2-methoxyacridine indicate that this reagent recognizes changes in the DNA conformation induced by RNA polymerase binding, in relation to open complex formation.

Aminoacridines↗
PubMed1988

Adenosine-guanosine preferential photocleavage of DNA by azido-benzoyl- and diazocyclopenta-dienylcarbonyloxy derivatives of 9-aminoacridine.

The photoreactions of 9-[6-(4-azidobenzamido)hexylamino]acridine (AHA) and 9-[6-(2-diazocyclopentadienylcarbonyloxy)hexylamino]acridine (DHA) with double stranded DNA result in formation of single strand nicks and alkali labile sites (adducts) with an efficiency of 6 x 10(-3) nicks per AHA and 3 x 10(-2) nicks per DHA molecule. The alkali dependent DNA cleavage by AHA shows a pronounced A+G preference whereas that by DHA is practically sequence independent. In the presence of diacridines, however, DHA exhibits a preference for cleavage at guanosines. These DNA photocleaving reagents could be useful for DNA photofootprinting and photosequencing.

Adenosine↗
PubMed1988

Sequence-influenced interactions of oligoacridines with DNA detected by retarded gel electrophoretic migrations.

We have found that di-, tri-, tetra-, and hexa-9-acridinylamines are so efficiently associated with DNA during electrophoresis in polyacrylamide or agarose gels that they retard its migration. The retardation is roughly proportional to the reagent to base pair ratio, and the magnitude of the retardation indicates that a combined charge neutralization/helix extension mechanism is mainly responsible for the effect. Furthermore, DNA sequence dependent differences are observed. Thus, the pUC 19 restriction fragments (HaeIII or AluI), which in the native state comigrate upon gel electrophoretic analysis, could be separated in the presence of a diacridine, and specific DNA fragments responded differently to different diacridines. These results suggest that the effect also is due to a contribution from the DNA conformation and that the DNA conformation dynamics are influenced differently upon binding of different diacridines. We foresee three applications of this observation: (1) in analytical gel electrophoretic separation of otherwise comigrating DNA molecules, (2) in studies of polyintercalator-DNA interaction, and (3) in measurements of polyintercalator-induced DNA unwinding.

Acridines↗
PubMed1988

9-Acridinylpeptides and 9-acridinyl-4-nitrophenylsulfonylpeptides. Synthesis, binding to DNA, and photoinduced DNA cleavage.

The preparation of 6-(9-acridinylamino)hexanoic acid DHBT ester and N alpha-Fmoc-N epsilon-(4-nitrophenylsulfonyl)-L-lysine DHBT ester and their application in solid phase peptide synthesis are described. The 9-acridinylamino ligand was shown to confer high DNA affinity, probably by intercalation, to the resulting peptides. The 4-nitrophenylsulfamido ligand furthermore resulted in "photonuclease" activity of some of the modified peptides.

Acridines↗
PubMed1986

Site specificity of psoralen-DNA interstrand cross-linking determined by nuclease Bal31 digestion.

A novel method for determination of psoralen photo-cross-linking sites in double-stranded DNA is described, which is based on a pronounced inhibition of Bal31 exonuclease activity by psoralen-DNA interstrand cross-links. The results using a 51 base pair fragment of plasmid pUC19 and a 346 base pair fragment of pBR322 show that 5'-TA sequences are preferred cross-linking sites compared to 3'-TA sequences. They also indicate that sequences flanking the 5'-TA site influence the cross-linking efficiency at the site. The DNA photo-cross-linking by 4,5',8-trimethylpsoralen and 8-methoxypsoralen was analyzed, and these two psoralens showed identical site specificity. The 5'-TA preference is rationalized on the basis of the local DNA structure in terms of the pi-pi electronic interaction between the thymines and the intercalated psoralens, as well as on the base tilt angles of the DNA.

Base Sequence↗
PubMed1986

Thermal chemistry of podophyllotoxin in ethanol and a comparison of the cytostatic activity of the thermolysis products.

Podophyllotoxin (1) in buffered ethanolic solution is degraded by two pathways. One leads to (a) picropodophyllin (2), which undergoes dehydration to give alpha-apopicropodophyllin (5), which rearranges to give beta-apopicropodophyllin (6), (b) the ethyl ether of picropodophyllotoxin, 8, and (c) the ethyl ether of epipicropodophyllotoxin, 7. The other pathway leads directly to epipodophyllotoxin (10) and the corresponding ethyl ether, 9, and possibly, via a transient 3,4-dehydropodophyllotoxin (5'), to beta-apopicropodophyllin (6). The 1H NMR spectra of these compounds are described, their in vitro cytostatic activity compared, and their syntheses, including that of podophyllotoxin ethyl ether, reported.

Antineoplastic Agents↗
PubMed1986

Protein crosslinking reagents containing a selenoethylene linker are cleaved by mild oxidation.

A homobifunctional cleavable crosslinking reagent containing a selenoethylene group in the linker, and related reagents, have been synthesized and tested in a model system involving formation of a complex between albumin and cytochrome c. Functionally, complex formation was suggested by albumin inhibition of the ascorbate reduction of cytochrome c. Structurally, complex formation was demonstrated by crosslinking and subsequent separation of crosslinked complex from non-crosslinked proteins by SDS-polyacrylamide gel electrophoresis. The crosslinks were found to be cleavable by mild oxidation with low concentrations of periodate or with N-chlorobenzenesulfonamide immobilized on polystyrene beads (Iodo-Beads).

Albumins↗