The structure of the unknown modified nucleoside Q, which is present in the first position of the anticodons of Escherichia coli tRNA Tyr, tRNA His, tRNA Asn, tRNA Asp, is proposed to be 7-(4,5-cis-dihydroxy-1-cyclopenten-3-ylaminomethyl)-7-deazaguanosine (1). The structure of Q was deduced by means of its uv absorption, mass spectrometry, proton magnetic resonance spectroscopy, and studies of its chemical reactivity. The structure of Q is unique since it is a derivative of 7-deazaguanosine having cyclopentenediol in the side chain at the C-7 position. This is the first example of purine skeleton modification in a nucleoside from tRNA.

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