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Scheme 3 | Sustainable Chemical Processes

Scheme 3

From: An astute synthesis of locked nucleic acid monomers

Scheme 3

Improved convergent synthesis of LNA monomers [ 20 , 21 ]. Reagents (% yields): (i) MsCl, pyridine, CH2Cl2 (98%); (ii) Ac2O, AcOH, conc. H2SO4 (97%); (iii) nucleobase, N,O-bis(trimethylsilyl)acetamide, TMS-triflate, CH3CN or 1,2-dichloroethane (18a, 90%; 18b, 88%; 18c, 68%; 18d, 82%); (iv) aq. NaOH, THF or dioxane (19a, 97%; 19b, 94%; 19c, 78%; 19d, 87%); (v) NaOBz, DMF (20a, 97%; 20b, 86%; 20c, 88%; 20d, 93%); (vi) aq. NaOH, THF (9a, 95%; 9b, 91%); NH4OH, MeOH (9c, 86%); (a) 20% Pd(OH)2-C, HCO2NH4, MeOH; (b) NH4OH (1d, 77%); (vii) 20% Pd(OH)2-C, 88% HCOOH, THF/MeOH (9:1) (1a, 91%); 20% Pd(OH)2-C, HCO2NH4, MeOH or EtOH (1b, 83%; 1c, 91%).

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