title: Synthesis of N3- and 2-NH2-substituted 6,7-diphenylpterins and their use as intermediates for the preparation of oligonucleotide conjugates designed to target photooxidative damage on single-stranded DNA representing the bcr-abl chimeric gene.
abstract: Two 17-mer oligodeoxynucleotide-5'-linked-(6,7-diphenylpterin) conjugates, 2 and 3, were prepared as photosensitisers for targeting photooxidative damage to a 34-mer DNA oligodeoxynucleotide (ODN) fragment 1 representing the chimeric bcr-abl gene that is implicated in the pathogenesis of chronic myeloid leukaemia (CML). The base sequence in the 17-mer was 3'G G T A G T T A T T C C T T C T T5'. In the first of these ODN conjugates (2) the pterin was attached at its N3 atom, via a -(CH2)3OPO(OH)- linker, to the 5'-OH group of the ODN. Conjugate 2 was prepared from 2-amino-3-(3-hydroxypropyl)-6,7-diphenyl-4(3H)-pteridinone 10, using phosphoramidite methodology. Starting material 10 was prepared from 5-amino-7-methylthiofurazano[3,4-d]pyrimidine 4 via an unusual highly resonance stabilised cation 8, incorporating the rare 2H,6H-pyrimido[6,1-b][1,3]oxazine ring system. In the characterisation of 10 two pteridine phosphazenes, 15 and 29, were obtained, as well as new products containing two uncommon tricyclic ring systems, namely pyrimido[2,1-b]pteridine (20 and 24) and pyrimido[1,2-c]pteridine (27). In the second ODN conjugate the linker was -(CH2)5CONH(CH2)6OPO(OH)- and was attached to the 2-amino group of the pterin. In the preparation of 3, the N-hydroxysuccinimide ester 37 of 2-(5-carboxypentylamino)-6,7-diphenyl-4(3H)-pteridinone was condensed with the hexylamino-modified 17-mer. Excitation of 36 with near UV light in the presence of the single-stranded target 34-mer, 5'T G A C C A T C A A T A A G14 G A A G18 A A G21 C C C T T C A G C G G C C3' 1 caused oxidative damage at guanine bases, leading to alkali-labile sites which were monitored by polyacrylamide gel electrophoresis. Cleavage was observed at all guanine sites with a marked preference for cleavage at G14. In contrast, excitation of ODN-pteridine conjugate 2 in the presence of 1 caused oxidation of the latter predominantly at G18, with a smaller extent of cleavage at G15 and G14 (in the double-stranded portion) and G21. These results contrast with our previous observation of specific cleavage at G21 with ruthenium polypyridyl sensitisers, and suggest that a different mechanism, probably one involving Type 1 photochemical electron transfer, is operative. Much lower yields were found with the ODN-pteridine conjugate 3, perhaps as a consequence of the longer linker between the ODN and the pteridine in this case.
authors.affiliation: Chemistry Department and Centre for Chemical Synthesis and Chemical Biology, Trinity College, University of Dublin, Dublin 2, Ireland.
authors.forename: Conor W
authors.initials: CW
authors.lastname: Crean
authors.forename: Russell
authors.initials: R
authors.lastname: Camier
authors.forename: Mark
authors.initials: M
authors.lastname: Lawler
authors.forename: Clarke
authors.initials: C
authors.lastname: Stevenson
authors.forename: R Jeremy H
authors.initials: RJ
authors.lastname: Davies
authors.forename: Peter H
authors.initials: PH
authors.lastname: Boyle
authors.forename: John M
authors.initials: JM
authors.lastname: Kelly
mesh_terms: D020029:Base Pairing; D001483:Base Sequence; D004249:DNA Damage; D004277:DNA, Single-Stranded / Q000737:chemistry* / Q000528:radiation effects; D016313:Genes, abl / Q000235:genetics* / Q000528:radiation effects; D006147:Guanine / Q000737:chemistry; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009841:Oligonucleotides / Q000737:chemistry; D016376:Oligonucleotides, Antisense / Q000138:chemical synthesis / Q000737:chemistry*; D017319:Photosensitizing Agents / Q000138:chemical synthesis / Q000737:chemistry; D011622:Pterins / Q000138:chemical synthesis* / Q000737:chemistry; D014466:Ultraviolet Rays
chemical_list: D004277:DNA, Single-Stranded; D009841:Oligonucleotides; D016376:Oligonucleotides, Antisense; D017319:Photosensitizing Agents; D011622:Pterins; D006147:Guanine