Solved: H. G. Khorana won the Nobel Prize in Medicine in 1968 for developing the

Chapter 0, Problem 23-73

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H. G. Khorana won the Nobel Prize in Medicine in 1968 for developing the synthesis of DNA and RNA and for helping to unravel the genetic code. Part of the chemistry he developed was the use of selective protecting groups for the OH group of nucleosides. 5 5-triphosphate, 13-azido-2,3-dideoxythymidine2, A + G = C + T? G = A? G = C A = T 13 end2 G-T-A-C 15 end2 2 3 HO base OH H2O ? OH O O 3 2 + H+ + The trityl ether derivative of just the OH group is obtained by reaction of the nucleoside with trityl chloride, MMT chloride, or DMT chloride and a base like The trityl ether derivative can be removed in dilute aqueous acid. DMT derivatives hydrolyze fastest, followed by MMT derivatives, and trityl derivatives slowest. (a) Draw the product with the trityl derivative on the oxygen. (b) Explain why the trityl derivative is selective for the OH group. Why doesnt it react at or (c) Why is the DMT group easiest to remove under dilute acid conditions? Why does the solution instantly turn orange when acid is added to a DMT derivative?