Detritylation

The acid treatment in each detritylation step may remove purines from deoxyriboses. Purine residues near the 3 -end will suffer the longest cumulative times of exposure to acid and therefore have the greatest chance for depurination . Thus each acid treatment should be as brief as possible. 

One synthesis cycle is now closed. A new cycle can start with 5 -detritylation (step 1). When the last cycle is closed, the terminal 5-0-(4,4 -dimethoxytrityl) group of the desired oligonucleotide is either removed or left attached before the deprotection, liberation and puriHcation of the product. 

Trityl Ethers. Treatment of sucrose with four molar equivalents of chlorotriphenylmethyl chloride (trityl chloride) in pyridine gives, after acetylation and chromatography, 6,1, 6 -tri-O-tritylsucrose [35674-14-7] and 6,6 -di-O-tritylsucrose [35674-15-8] in 50 and 30% yield, respectively (16). Conventional acetylation of 6,1, 6 -tri-O-tritylsucrose, followed by detritylation and concomitant C-4 to C-6 acetyl migration using aqueous acetic acid, yields a pentaacetate, which on chlorination using thionyl chloride in pyridine and deacetylation produces 4,l, 6 -trichloro-4,l, 6 -trideoxygalactosucrose [56038-13-2] (sucralose), alow calorie sweetener (17). 

Next nucleotide added following detritylation as in Step 1. Cycle repeated to syndiesize oligonucleotide of desired sequence and length. 

These ligands can readily be obtained by a Grignard reaction of aziridine esters, followed by an acidic detritylation (see Scheme 40) [19,55]. These aziridine carbinol-derived catalysts are equally efficient as the Corey ligand 55 derived from proline carbinols (Fig. 4) [55,56]. 

Glycosylation of the 7-hydroxy compound, prepared from 367 by trityla-tion, benzylation, and detritylation with acid, afforded the protected validamycin D in good yield. 

The detritylation of N-tryphenylmethylvaleric acid ester derivatives was accomplished by catalytic hydrogenolysis, both in the standard and catalytic transfer modes.338 The trityl precursor was suspended in a mixture of EtOH and AcOH, and HC02NH4 was added. Reduction began with the addition of 10% Pd/C (0.05 mol Pd/mol) and continued for 50 hours at 25°C. 

On treatment with dimethyl sulfoxide-acetic anhydride followed by sequential oximation, reduction, detritylation, and acid hydrolysis, a tetra-(6-0-trityl)-cyclohexaamylose was reported to afford 2-amino-2-deoxy-D-glucose, in addition to D-glucose, indicating459 that... 

Similar results were obtained when detritylation of 2,3,4,1, 3, 4 -hexa-0-acetyl-6,6 -di-0-tritylsucrose (37) and 2,3,4,l, 3, 4 -hexa-0-... 

O-trityl-D-gaIactono-1,4-lactone (30c). Detritylation of 30c with F3B OEt2 caused 0-5 —> 0-6 acetyl migration, affording 30b, which was used for the preparation of 5-O-methyl-D-galactofuranose (39). 

FIGURE 6.30 Approaches for the synthesis of monosubstituted trifunctional amino acids. (A) Monoesterification of dicarboxylic acids. (B) Aa-Alkoxycarbonylation of lysine through the e-benzylidene derivative [Bezas Zervas, 1963]. (C) SelectiveN -detritylation of ditrityl derivatives.138 (D) A- AI ko x y met hy 1 at 10 n of histidine by displacement of AP-substituents.137 Cbz-His(CH2OR)-OMe are obtained from Cbz-His(xAc)-OMe. = Acylating reagent. 

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