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K Lesiak

Publications and source records attributed to K Lesiak.

43 records · Page 3Linked to original sources
PubMed1982

Oligonucleotide structural features involved in binding to and activation of the 2-5A-dependent endoribonuclease of L cells.

Several analogues of 2-5A were prepared and evaluated for their ability to bind to and/or activate the 2-5A dependent endonuclease from murine L cells. Replacement of one of the two 2',5'-phosphodiester bonds of ppp5'A2'p5'A2'p5'A with 3',5'-phosphodiester bonds gave analogues 40-50 X less active than 2-5A in binding to or activation of the 2-5A-activated endonuclease whereas replacement of both 2',5'-linkages with 3',5'-linkage resulted in a compound (3-5A) which was 10,000 X less effective in binding to the endonuclease and devoid of activity as an inhibitor of protein synthesis. The sequence of periodate oxidation/Schiff base formation/borohydride reduction gave a derivative of ppp5'A2'p5'A2'p5'A2'p5'A in which the 2'-terminal ribose was replaced with a N-hexyl morpholine ring. This material was 10 X more active than 2-5A an a inhibitor of translation. One possible explanation for this increased activity is that the 2'-terminally modified oligomer is resistant to degradation by the 2',5'-phosphodiesterase responsible for the degradation of 2-5A in cell extracts.

Adenine Nucleotides↗
PubMed1979

Stereochemistry of hydrolysis of adenosine 3':5'-cyclic phosphorothioate by the cyclic phosphodiesterase from beef heart.

Adenosine 3':5'-cyclic phosphorothioate, Sp-diastereomer was hydrolyzed by cyclic phosphodiesterase from beef heart in the presence of [18O]water to [18O]adenosine 5'-phosphorothioate. This was phosphorylated by myokinase and pyruvate kinase to [18O]adenosine 5'-(1-thiotriphosphate),Sp-diastereomer. The position of 18O was determined to be in a nonbridging position. This result indicates that the hydrolysis proceeded with inversion of configuration at phosphorus.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMedDate not supplied

2',5'-Oligoadenylate:antisense chimeras--synthesis and properties.

We have synthesized a novel bioconjugate which joins an antisense oligonucleotide to a unique and potent inhibitor of translation,pn5'A2'(p5'A2')mp5'A(2-5A). Two residues of 4-hydroxybutyl phosphate were employed as linkers to attach the 2',5'-oligoadenylate moiety through its 2'-terminus to the 5'-terminus of the chosen antisense sequence, (dT)20. The syntheses were carried on a solid support according to the phosphite triester method of DNA synthesis (Letsinger, R.L., Lunsford, W.B. (1976) J. Am. Chem. Soc. 98, 3655-3661; Beaucage, S.L., and Caruthers, M.H. (1981) Tetrahedron Lett. 22, 1859-1862). The generated 2-5A antisense chimeras retained both the ability of the 2-5A molecule to activate the 2-5A-dependent RNase as well as the ability of the oligo(dT) moiety to hybridize to the complementary poly(A). Moreover, the chimera, when annealed to its target nucleic acid sequence, was still effectively bound to the 2-5A-dependent nuclease. The methodology described represents a new approach to the selective modulation of mRNA expression.

Adenine Nucleotides↗
PubMedDate not supplied

Efficient functionalization of 2',5'-oligoadenylates with sulfur.

To derivatize the 2'-terminus of 2',5'-oligoadenylates with a thiol group, the reaction of periodate-oxidized nucleotide and 2',5'-oligonucleotide with aminothiols was explored. Two separate synthetic approaches were employed, both of which relied upon the use of S-protected thiols. In one approach, 5'AMP was oxidized with sodium periodate to dialdehyde, which was reacted with cystamine hydrochloride. Sodium cyanoborohydride reduction of the unisolated intermediate animal gave compound 4. The second approach involved reaction of S-(2-tetrahydropyranyl)cysteamine with the dialdehyde obtained by periodate oxidation of 5'AMP to yield, after reduction with Na(CN)BH3, the S-protected adduct 3. Intermediate 3 could be oxidized with aqueous iodine to give disulfide 4. Disulfide 4, obtained by either of the above routes, was reduced with dithiotreitol (DTT) to the thiol 5. This same reaction sequence was applied to 2-5A tetramer monophosphate, p5'A2'[p5'A2']2p5'A (6a), to give via 6b the 2'-terminal-modified derivative 6c. Aqueous iodine oxidation of 6c provided the disulfide 7, which reacted with DTT to give quantitative conversion to product, the free thiol 8. Both the disulfide 7 and the S-tetrahydropyranyl-protected derivative (6c) were bound effectively to the 2-5A-dependent RNase L of mouse L cells with IC50 values of 1 x 10(-9) M for 7 and 8 x 10(-10) M for 6c, not significantly different from the corresponding value for the parent unmodified 2-5A (6a) itself.

Adenine Nucleotides↗