- D The Following Sequence Represents A Typical Preparation And Activation Of A Thioglycoside Donor In Carbohydrate Synt 1 (245.06 KiB) Viewed 62 times
(d) The following sequence represents a typical preparation and activation of a thioglycoside donor in carbohydrate synthesis Write structures B-D and the mechanism for the formation of D. (20) Question 1 continues on the following page... Page 2 of 6 OH EISH Ac,O (>5 eq) D-Glucose B pyridine с D BF, ELO NIS/AGOTT NIS = N-iodosuccinimide AgOTI = silver trifluoromethanesulfonate (e) Ribonucleosides can be converted into 2'-deoxyribonucleosides as follows. Suggest the reaction mechanism for step 1. (20) NH NH CH,COBI HBr/HOÁC NH Bu,SnH AIBN HOS O AcO Aco step 1 step 2 OH OH OAc Br OAc () Structure E is a key intermediate in phosphotriester approach for the synthesis of oligonucleotides. Its synthesis is shown below. Answer all sections (0) - (iii) relating to this synthesis. (20) - DMTro DMTIO CN MS-CI, Py HO OH -CN MS-CI, 2,4,6-Trimethylbenzenesulfonyl chloride Py, Pyridine E B = nucleobase () Draw the structure of the DMT protecting group. (3) (il). Propose a mechanism for the formation of E. (10) (ii) The B-cyanoethyl group is often used as a phosphate protecting group. Give the mechanism for its removal by aqueous ammonia (7)