Benzyl esters acid effect

N -Fmoc serine benzyl ester 2, which could be prepared as shown or purchased commercially, was smoothly converted to the crystalHne O-methylthiomethyl (MTM) ether 3 in high yield via a Pummerer-Hke reaction using benzoyl peroxide and dimethyl sulfide in acetonitrile [39]. This common intermediate was used to synthesize both 5 and 8 [40]. Both Ogilvie [41] and Tsantrizos [42] had reported that I2 was an effective activator with similar MTM ether substrates. The H promoted nucleosidation reaction between O-MTM ether 3 and bis-silylated thymine 4 produced the nucleoamino acid 5 in 60% isolated yield (100% based on recovered 3). Hydrogenolytic deprotection of the benzyl ester with H2, Pd/C in MeOH gave the thymine-containing nucleoamino acid 6 in quantitative yield. 

A variant that eliminates the production of water and that has proved effective for esterification of hydroxy and aromatic amino acids involves the use of thionyl chloride instead of acid. At a low temperature, the alcohol reacts with the chloride, generating methyl sulfinyl chloride, which produces the ester, probably through the mixed carboxylic acid-sulfinic acid anhydride (Figure 3.18, B). p-Toluenesulfonyl chloride added to the acid and benzyl alcohol serves the same purpose in the preparation of benzyl esters. 

We thus turned to a study of the effect of substituting a methyl group on the activity of a set of meta substituted benzyl esters that closely resembled the original data set. Most of our original work was done on monosubstituted benzyl esters of DVA while during later work we concentrated our efforts on the generally more active cis-3-(2-chloro-3,3,3-trifluoro-l-propenyl)-2,2-dimethylcycopropanecarboxylic acid (TFP) esters. In order to include more compounds in com-... 

Hyper-branched polymers are prepared in a single-step polymerization from ABX monomers. Thus, a perfectly branched structure is present in dendrimers, whereas irregular branching is present in hyper-branched polymers. Aluminum alkoxide-based initiators or tin-based catalysts have been successfully used for the preparation of, hyper-branched [160-162, 166-168], dendrimer-like star polymers [160], and star-shaped polymers. The first and second generations of the benzyl ester of 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) are effective initiators for the ROP of lactones (e-CL) in the presence of Sn(Oct)2. The... 

Now see what happens if we replace the achiral benzyl ester group with an amide derived from the natural amino acid valine (Chapter 49). The diastereoselectivity remains the same but the chiral environment created by the single enantiomer covalently bonded to the dienophile has a remarkable effect only one enantiomer of the product is formed. 

Esterification catalyst. Sulfuryl chloride is an effective esterification catalyst, particularly useful for peptides since no racemization occurs."" The N-acylated amino acid or peptide is dissolved in methanol containing a trace of the catalyst, and the mixture is allowed to stand for 48 hrs. at 20°. Yields are generally in the range 85-95%. Benzyl esters are prepared similarly except that sy m-tetrachloroethane is used as solvent. 

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