The stereocontrolled synthesis of the extremely labile phthalic acid 4,5-cis-dihydrodiol(l) has been achieved in a highly efficient manner in seven step from bis[2-(trimenyleiethyl] fumarate (2). The Diela-Alder adduct 3 of the fumarate with furan has been converted into first em-cis-diol 4 and then ita acetonide 5. Treatment of acetonide 5 with lithium hexamethyldisilazide resulta in the regioselective formation of olefinic alcohol 6. Following the introduction of the second double bond into the cyclohexene ring system, the highly sensitive deprotection of the acetonide group of dihydrodiol diester acetonide 7 can be effected under iodine catalysis. The hydrolysis of the 2-(trimethylsily1)ethyl ester group has been achieved by treatment with tetra(n-butyl)ammonium fluoride in THF. This synthesis constitutes an unambiguous assignment of the structure and stereochemistry of the microbial metabolite of phthalic acid. (7) H a " , A.; Alexanian, V. Tetrahedron Lett. 1978,4475.A strategy is described for synthesis of oligomers modified in the 4-position of thymine by postsynthetic substitution. 4-Triamlothymine phoephoramidite monomer has been prepared in one step from thymine amidite monomer and incorporated into a 12 mer AGCGAAXTCGCT using a DNA-synthesizer. The fully protected oligomer containing 4-triazolothymine, while still bound to CPG-support, was treated at 25 "C with either alcohol/DBU, dilute aqueous NaOH, concentrated aqueous ammonia, 1,l-dimethylhydrazine, or thiolacetic acid, to produce essentially pure oligodeoxynucleotides containing @-alkylthymine, thymine, 5-methylcytosine, N4-(dimethylamino)-5-methylcytosine [i.e., 4-(2,2-dimethylhydrazino)-5-methylpyrimid-2-one (TDH)], or 4thiothymine respectively. Thie f i t and efficient synthesis of TDH oligomers indicates that this may be a general route to the synthesis of oligomers containing thymine with a reactive group at the 4-position. The melting temperature (Tm) of a DNA duplex containing TDH:G or TDH:A pairs was similar to that of a duplex with AC mismatch.
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