Trityl groups

Ph3CCl, 2,4,6-collidine, CH2CI2, Bu4N" C104, 15 min, 97% yield. This is an improved procedure for installing the trityl group on polymer-supported nucleosides. 

The trityl group can migrate from one secondary center to another under acid catalysis. ... 

Ph3COSiMc3, Me3SiOTf, CH2CI2, 0°, 0.5 h, 73-97% yield. These conditions will also introduce the trityl group on a carboxyl group. The primary hydroxyl of persilylated ribose was selectively derivatized. 

CF3COOH, r-BuOH, 20°, 2-30 min, then Bio-Rad 1x2 (OH ) resin.These conditions were used to cleave the trityl group from the 5 -hydroxyl of a nucleoside. Bio-Rad resin neutralizes the hydrolysis and minimizes cleavage of,glycosyl bonds. 

Et2AlCl, CH2CI2, 3 min, 70-85% yield.This method was used to remove the trityl group from various, protected deoxyribonucleotides. The TBDPS group is stable to these conditions. 

These were originally prepared by Khorana as selective protective groups for the 5 -OH of nucleosides and nucleotides. They were designed to be more acid-labile than the trityl group because depurination is often a problem in the acid-catalyzed removal of the trityl group. Introduction of p-methoxy groups increases the rate of hydrolysis by about one order of magnitude for each p-methoxy substituent. For 5 -protected uridine derivatives in 80% AcOH, 20°, the time for hydrolysis was... 

Acetone, CUSO4, H2SO4, 90% yield.If PPTS replaces H2SO4 as the acid, the acetonide can be formed in the presence of a trityl group. 

Tetrazole, trifluoroethanol, 24 h, 95% yield. These conditions will also cleave the A-trityl group. If deprotection is performed in the presence of an acylating agent, acylation proceeds directly. 

This group was reported to be 6000 times more stable to acid than the trityl group because of destabilization of the cation by the fluorenyl group. 

The first objective was the conversion of L-tryptophan into a derivative that could be converted to pyrroloindoline 3, possessing a cis ring fusion and a syn relationship of the carboxyl and hydroxyl groups. This was achieved by the conversions shown in Scheme 1. A critical step was e. Of many variants tried, the use of the trityl group on the NH2 of tryptophan and the t-butyl group on the carboxyl resulted in stereospecific oxidative cyclization to afford 3 of the desired cis-syn stereochemistry in good yield. 

The conversion of 3 to 8 is summarized in Scheme 2. The trityl group (too large and too acid sensitive for the ensuing steps) was removed from N, and both N s were protected by Cbz (benzyloxycarbonyl) groups. Protection of the tertiary OH specifically as the robust TBS (f-butyldimethylsilyl) group was found to be necessary for the sequence involving the electrophilic aromatic substitution step, 5 to 6, and the Stille coupling steps (6 + 7 —> 8). 

BCI3-DMS, CH2CI2, 5 min —> 24 h, rt, 16-100%." A trityl group is cleaved in preference to a benzyl group under these conditions. 

CF3COOH, TFAA, CH2CI2. These conditions afford the trifluoroacetate, thus preventing retritylation, which is sometimes a problem when a trityl group is cleaved with acid. A further advantage of these conditions was that a SEM group was completely stable. When TFAA was not used. 

The following is an example of the use of the MMTr group in a nonnucleoside setting where the usual trityl group was too stable ... 

Under these conditions, the trityl group has an estimated t,/2 of -320 min. 

For a review in which the use of various trityl groups in nucleotide synthesis is discussed in the context of the phosphoramididite approach, see S. L. Beaucage and R. P. Iyer, Tetrahedron, 48, 2223 (1992). 

H2O2, CI3CCO2H, CH2CI2, -BuOH dimethyl sulfide, 80% yield. Other methods cleaved the epoxide. This method also cleaves the THP and trityl groups. 

The Dcpm group can be removed in the presence of a -butyl or A-trityl group with 1% TFA in CH2Cl2. ... 

The trityl group was introduced on a primary amide, RCONH2, in the presence of a secondary amide with TrOH, AC2O, H2SO4, AcOH, 60°, 75% yield. It is stable to BOC removal with 1 N HCl in 50% isopropyl alcohol, 30 min, 50°, but can be cleaved with TFA. The following table gives the cleavage rates with TFA for a number of protected primary amides. 

In subsequent studies,22 Sheehan et al. demonstrated that the action of diisopropylcarbodiimide on penicilloate 24, prepared by protection of the free primary amino group in 23 with trityl chloride (see Scheme 6b), results in the formation of the desired -lactam 25 in a very respectable yield of 67 %. In this most successful transformation, the competing azlactonization reaction is prevented by the use of a trityl group (Ph3C) to protect the C-6 amino function. Hydrogenolysis of the benzyl ester function in 25, followed by removal of the trityl protecting group with dilute aqueous HC1, furnishes 6-aminopenicillanic acid (26), a versatile intermediate for the synthesis of natural and unnatural penicillins. 

The primary OH group can be selectively blocked by the bulky triphenyl-methyl (trityl) moiety, followed by esterification at the secondary OH groups and removal of the protecting trityl group. Thus 2,3-di-O-acetyl cellulose has been obtained by this procedure. Moreover, regioselectively substituted mixed cellulose esters, acetate/propionate, were prepared by subsequent acy-... 

This result is in strong contrast with that obtained by Tanner et al. [49] for ligand 52 (ee of 2% for the addition of diethylzinc to benzaldehyde. Fig. 3). It was argued by Tanner that the M-trityl group would be too large to allow efficient chelate formation with diethylzinc [49], which is however clearly not the case... 

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