<p>Cyclobutane pyrimidine dimers
(CPD) are the predominant DNA lesions formed upon exposure of this biopolymer
to sunlight. Given the potentially dire biological consequences of DNA lesions,
there is a need to fully characterize their behaviour, with an eye towards understanding
their complete reactivity and as a possible means to detect and quantify their presence
in the genome. The work described in this dissertation describes studies of the
alkaline reactivity of CPD lesions generated within dinucleotide &
polynucleotide strands. It was found that CPD-TpT is generally inert under alkaline
conditions at room temperature, which is in agreement with earlier studies on
alkaline hydrolysis of CPD-thymine and CPD-thymidine. However, a re-evaluation
of the same reaction in the presence of <sup>18</sup>O labelled water
demonstrated that, similar to other UV-induced DNA lesions containing a
saturated pyrimidine ring, CPD undergoes a water addition at the C4=O group of
the nucleobase leading to the formation of a hemiaminal intermediate. This
intermediate, however, does not lead to hydrolysis products and completely
reverts to starting material under those same conditions. Moreover, the two
C4=O groups present on 3′ and 5′-thymines in a CPD molecule show different chemical
reactivities, with the 3′ C4=O group having greater affinity towards water
addition as compared to the one on 5′ end, a fact reflected in different rates
of exchange with the incoming nucleophile leading to the hemiaminal
intermediate. The <sup>18</sup>O labelling reaction was also investigated in
CPD lesions generated within oligonucleotides to probe the cause of asymmetry between
the 3′ <i>vs</i> 5′ C4=O groups; ultimately,
it was determined that the asymmetric reactivity observed to occur between the
two C4=O groups was an intrinsic property of the CPD molecule and did not arise
as a result of asymmetry in a dinucleotide setting.</p><p><br></p>
<p>In addition to the above studies,
during the course of the investigation of the nucleophilic reactivity of CPD, a
chemical reaction was observed leading to what appeared to be the rapid and
total chemical reversal of CPD lesions to the original TpT (thymine-thymine
dinucleotide)! This “repair” reaction occurred when CPD reacted with hydrazine,
and appears facilitated by an inert atmosphere under which it rapidly proceeds
to completion at room temperature.</p><br>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/13368785 |
| Date | 07 January 2021 |
| Creators | Ritu Chaturvedi (9760955) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/Reactivities_Leading_to_Potential_Chemical_Repair_of_Sunlight-Induced_DNA_Damage_Mechanistic_Studies_of_Cyclobutane_Pyrimidine_Dimer_CPD_Lesions_under_Alkaline_Conditions/13368785 |
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