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

An efficient method of ureido linkage formation during epimerization-free one-pot synthesis of protected hypermodified N-6-threonylcarbamoyladenosine (t(6)A) and its 2-SMe analog (ms(2)t(6)A) was developed. The method is based on a Tf2O-mediated direct conversion of the N-Boc-protecting group of N-Boc-threonine into the isocyanate derivative, followed by reaction with the N(6)exo-amine function of the sugar protected nucleoside (yield 86-94%). Starting from 2 ',3 ',5 '-tri-O-acetyl protected adenosine or 2-methylthioadenosine, the corresponding 3 '-O-phosphoramidite monomers were obtained in 48% and 42% overall yield (5 step synthesis). In an analogous synthesis, using the 2 '-O-(tert-butyldimethylsilyl)-3 ',5 '-O-(di-tert-butylsilylene) protection system at the adenosine ribose moiety, the t(6)A-phosphoramidite monomer was obtained in a less laborious manner and in a remarkably better yield of 74%.

Automated summary

An efficient method of ureido linkage formation was developed for the epimerization-free one-pot synthesis of protected hypermodified N-6-threonylcarbamoyladenosine and its 2-SMe analog. Starting from different protected adenosine derivatives, the corresponding 3'-O-phosphoramidite monomers were successfully obtained.