Investigation of Sulfur-related Influences on the Construction and Ring Opening of a Six-membered Cyclic Xanthate Derived from d‑Thymidine and CS₂

Structural characterization by MALDI-TOF mass spectrometry and NMR spectroscopy of polymers obtained from ROPs of 3′,5′-cyclic <i>N</i>³-(3-butenyl)-d-thymidine <i>trans</i> xanthate conducted at or somewhat below ambient temperatures indicated the presence of linear and cyclic species having primarily dimeric 5′,5′-trithiocarbonate-<i>co</i>-3′,3′-thionocarbonate connectivities from an alternating C–S and C–O cleavage pathway.

Other minor trithiocarbonate, xanthate, and thionocarbonate functionalities were proposed to arise from backbiting reactions and/or minor regiorandom cleavages. In contrast, ROPs conducted at reduced temperatures (≤ −20 or −40 °C depending on the organobase) achieved selective C–S cleavage to yield 3′,5′-xanthate-connected polymers of <i>N</i>³-(3-butenyl)-d-thymidine with more structural similarity to native DNA.

These fundamental advances extend the breadth of nucleoside-derived polymers, emphasizing the influence of sulfur incorporation during monomer synthesis and upon subsequent ROPs, with outcomes being temperature-mediated alternating vs. unidirectional backbone compositional and structural regioregularity.