Abstract
Promutagenic O6-alkylguanine adducts in DNA are repaired in humans by O6-methylguanine-DNA-methyltransferase (MGMT) in an irreversible reaction. Here we describe the synthesis of a phosphoramidite that allows the preparation of oligodeoxyribonucleotides (ODNs) containing a novel tricyclic thio analogue of O6-methylguanine in which the third ring bridges the 6-thio group and C7 of a 7-deazapurine. These ODNs are very poor substrates for MGMT and poorly recognised by the alkyltransferase-like protein, Atl1. Examination of the active sites of both MGMT and Atl1 suggest large steric clashes hindering binding of the analogue. Such analogues, if mutagenic, are likely to be highly toxic.
Highlights
The exposure of DNA to alkylating agents can result in the formation of toxic, pro-mutagenic O6-alkylguanine (O6-alkG) adducts (e.g., Figure 1)
We describe the synthesis of a phosphoramidite that allows the preparation of oligodeoxyribonucleotides (ODNs) containing a novel tricyclic thio analogue of O6-methylguanine in which the third ring bridges the 6-thio group and C7 of a 7-deazapurine
Insertion of thymine opposite O6-alkGs during DNA replication can result in GC->AT transition mutations, that are a common feature of many tumours[1] and In humans the protein O6-methylguanine-DNA-methyltransferase (MGMT) repairs O6-methylguanine [O6-MeG (1)] and other O6-alkGs via the irreversible transfer of the alkyl group to Cys145, thereby reforming guanine and inactivating the protein.[2]
Summary
In common with MGMT, the highly homologous alkyltransferase-like (ATL) proteins recognise O6-alkG adducts in DNA.[16,17] since they lack a nucleophilic Cys (which is typically replaced by Trp or Ala) they bind to, but do not de-alkylate these adducts Adduct recognition by both MGMT and ATL proteins requires flipping of the base adduct into the active site. We found that ODNs containing compound 8 were completely refractory to repair by MGMT.[21] We reasoned that this might be due to the locked anti or proximal conformation of the alkyl group (pointing away from the hydrogen bonding face) This would place Cys145 in MGMT in an unfavourable trajectory for nucleophilic addition to the electrophilic carbon attached to the heteroatom. We describe the synthesis of the 20-deoxyribonucleoside of 9, its incorporation into ODNs and the properties of these ODNs as substrates for both MGMT and Atl
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
