Identification and structure determination of a third cyclobutane photodimer of thymidylyl-(3'-->5')-thymidine: the trans-syn-II product.
Photolysis of thymidylyl-(3'-->5')-thymidine (TpT) has been previously reported by many workers to lead to only two cyclobutane dimers, the cis-syn and trans-syn-I dimers. This is curious in light of the fact that photolysis of thymidylyl-(3'-->5')-deoxyuridine (TpdU), which has a hydrogen in place of a methyl group at C6 of the 3'-thymidine, produces two trans-syn diastereomers. Recently, we discovered by way of X-ray crystallography that photolysis of the (Rp)-methyl phosphate ester of TpT leads to two trans-syn diastereomers, prompting us to reexamine the photochemistry of TpT. In this paper we show that sensitized photolysis of TpT also leads to the hitherto unknown trans-syn-II diastereomer in 2% yield. We also report the solution-state 1H NMR assignment of the trans-syn-II photodimer of TpT and its (Rp)-methyl phosphate ester by way of 2D homonuclear Hartmann--Hahn experiment, rotating frame nuclear Overhauser effect spectroscopy, and proton-detected 1H-31P correlation spectroscopy. Conformational analysis of three-bond 1H-1H, 1H-31P, and 13C-31P coupling constant data established a close similarity between the solution-state structures of the trans-syn-II photodimer of TpT and its (Rp)-methyl phosphate ester, with the crystal structure of the methyl phosphate ester.
Kao
J L
JL
Department of Chemistry, Washington University, St. Louis, Missouri 63130.
Nadji
S
S
Taylor
J S
JS
D003503:Cyclobutanes / Q000737:chemistry*; D015226:Dinucleoside Phosphates / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D010777:Photochemistry; D011740:Pyrimidine Dimers / Q000737:chemistry*; D013237:Stereoisomerism; D014961:X-Ray Diffraction
D003503:Cyclobutanes; D015226:Dinucleoside Phosphates; D011740:Pyrimidine Dimers; C017758:thymidylyl-(3'-5')-thymidine