Synthesis of the Anticodon HairpintRNAfMet ContainingN-{[9-(β-D-Ribofuranosyl)-9H-purin-6-yl]carbamoyl}-L-threonine (=N6-{{[(1S,2R)-1-Carboxy-2-hydroxypropyl]amino}carbonyl}adenosine, t6A)

Abstract

As part of our studies on the structure of yeast tRNAfMet, we investigated the incorporation of N‐{[9‐(β‐D‐ribofuranosyl)‐9H‐purin‐6‐yl]carbamoyl}‐L‐threonine (t6A) in the loop of a RNA 17‐mer hairpin. The carboxylic function of the L‐threonine moiety of t6A was protected with a 2‐(4‐nitrophenyl)ethyl group, and a (tert‐butyl)dimethylsilyl group was used for the protection of its secondary OH group. The 2′‐OH function of the standard ribonucleotide building blocks was protected with a [(triisopropylsilyl)oxy]methyl group. Removal of the base‐labile protecting groups of the final RNA with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) and then with MeNH2 was done under carefully controlled conditions to prevent hydrolysis of the carbamate function, leading to loss of the L‐threonine moiety.

Efficient access to 3′-O-phosphoramidite derivatives of tRNA relatedN6-threonylcarbamoyladenosine (t6A) and 2-methylthio-N6-threonylcarbamoyladenosine (ms2t6A)

“… 29,34–40 Initially, the isocyanate derivative was generated from the N 6 -amine function of sugar protected adenosine ( Scheme 1 , path B1), but its condensation with the free amine function of l -threonine was ineffective and the ureido-nucleoside product was obtained in a low 19% yield. 43 Noticeably better results were obtained in our recently published method ( Scheme 1 , path B2), based on the reaction of isocyanate derivative of the amino acid substrate (prepared by removing of Boc-protection and phosgene treatment of the free amine function of l -threonine appropriately blocked on the OH and COOH functions) with the sugar protected nucleoside (overall yield of this three steps procedure ∼55%). 39 This result of isocyanate procedure turned our attention to the methods of synthesis of unsymmetrical ureas involving the formation of the isocyanate functionality directly from the carbamate type protecting groups of amino acids ( e.g.…”