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Scheme 5 | Sustainable Chemical Processes

Scheme 5

From: An astute synthesis of locked nucleic acid monomers

Scheme 5

Chemo-enzymatic convergent synthesis of 2'-O ,4'-C-methylene-ribonucleosides (LNA monomers) 1a-d [ 24 ]. Reagents & conditions (% yields): (i) TsCl, pyridine, CH2Cl2, 0°C to rt (98%); (ii) Ac2O, AcOH, H2SO4 (100:10:0.1), 0°C to rt (97%); (iii) nucleobase, N,O-bis(trimethylsilyl) acetamide, TMS-triflate, acetonitrile or 1,2-dichloroethane, 80°C (24a, 89%; 24b, 88%; 24c, 71%; 24d, 78%); (iv) aq. NaOH, 1,4-dioxane, rt (+NH4OH for 9c) (9a, 95%; 9b, 93%; 9c, 89%; 9d, 94%); (v) 20% Pd(OH)2-C, HCOOH, THF:MeOH (9:1), reflux (1a, 91%); 20% Pd(OH)2-C, HCO2NH4, MeOH or EtOH, reflux (1b, 83%; 1c, 91%; 1d, 81%).

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