Leif Christensen

Peptide nucleic acids (PNA) were synthesized by a modified Merrifield method using several improvements. Activation by O-[benzotriazol-1-yl]-1,1,3,3-tetramethyluronium hexafluorophosphate in combination with in situ neutralization of the resin allowed efficient coupling of all four Boc-protected PNA monomers within 30 min. HPLC analysis of the crude product obtained from a fully automated synthesis of the model PNA oligomer H-CGGACTAAGTCCATTGC-Gly-NH2, indicated an average yield per synthetic cycle of 97.1%. N1-benzyloxycarbonyl-N6(3)-methylimidazole triflate substantially outperformed acetic anhydride as a capping reagent. The resin-bound PNAs were successfully cleaved by the 'low-high' trifluoromethanesulphonic acid procedure.

The synthesis and DNA binding properties of bis-PNA (peptide nucleic acid) are reported. Two PNA segments each of seven nucleobases in length were connected in a continuous synthesis via a flexible linker composed of three 8-amino-3,6-dioxaoctanoic acid units. The sequence of the first strand was TCTCTTT (C- to N-terminal), while the second strand was TTTCTCT or TTTJTJT, where J is pseudoisocytosine. These bis-PNAs form triple-stranded complexes of somewhat higher thermal stability than monomeric PNA with complementary oligonucleotides and the thermal melting transition shows very little hysteresis. When the J base is placed in the strand parallel to the DNA complement ('Hoogsteen strand'), the DNA binding was pH independent. The bis-PNAs were also superior to monomeric PNAs for targeting double-stranded DNA by strand invasion.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSynthesis of Peptide Nucleic Acid Monomers Containing the Four Natural Nucleobases: Thymine, Cytosine, Adenine, and Guanine and Their OligomerizationKim L. Dueholm, Michael Egholm, Carsten Behrens, Leif Christensen, Henrik F. Hansen, Tore Vulpius, Kenneth H. Petersen, Rolf H. Berg, Peter E. Nielsen, and Ole BuchardtCite this: J. Org. Chem. 1994, 59, 19, 5767–5773Publication Date (Print):September 1, 1994Publication History Published online1 May 2002Published inissue 1 September 1994https://pubs.acs.org/doi/10.1021/jo00098a042https://doi.org/10.1021/jo00098a042research-articleACS PublicationsRequest reuse permissionsArticle Views3785Altmetric-Citations265LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

The thermodynamics of hybridization and the conformations of decameric mixed purine-pyrimidine sequence PNA/PNA, PNA/DNA, and DNA/DNA duplexes have been studied using fluorescence energy transfer (FET), absorption hypochromicity (ABS), isothermal titration calorimetry (ITC), and circular dichroism (CD) techniques. The interchromophoric distances determined in the FET experiments on fluorescein- and rhodamine-labeled duplexes indicate that the solution structures of the duplexes are extended helices in agreement with available NMR (PNA/DNA) and crystal X-ray data (PNA/PNA). The melting thermodynamics of the duplexes was studied with both FET and ABS. The thermodynamic parameters obtained with ABS are in good agreement with the parameters from calorimetric measurements while FET detection of duplex melting gives in most cases more favorable free energies of hybridization. This discrepancy between FET and ABS detection is ascribed to the conjugated dyes which affect the stability of the duplexes substantially. Especially, the dianionic fluorescein attached via a flexible linker either to PNA or to DNA seems to be involved in an attractive interaction with the opposite dicationic lysine when hybridized to a PNA strand. This interaction leads to an increased thermal stability as manifested as a 3-4 degreesC increase of the melting temperature. For the PNA/DNA duplex where fluorescein is attached to the PNA strand, a large destabilization (DeltaTm = -12 degreesC) occurs relative to the unlabeled duplex, probably originating from electrostatic repulsion between the fluorescein and the negatively charged DNA backbone. In the case of the PNA/PNA duplex, the sense of helicity of the duplex is reversed upon conjugation of fluorescein via a flexible linker arm, but not when the fluorescein is attached without a linker to the PNA.