Monobenzyl protection

The cyclohexylidene protecting group has been employed in several syntheses. A preparation of 2,3-0-cyclohexylidene-4-deoxy-L-threose (445) fi om L-( + )-diethyltartrate (lb) in seven steps illustrates one synthetic application (Scheme 99). Conversion of the monobenzyl protected alcohol 443 to its tosylate followed by reduction with sodium borohydride provides the deoxy intermediate 444, which is reductively deprotected and Swem oxidized to 445 in good overall yield. Treatment with benzylamine provides an imine that undergoes a stereoselective carbon-carbon bond forming reaction with a-lithio-A, A -dimethylacetamide in the presence of the Lewis acid zinc bromide to furnish, after Cbz-amine protection, the j9-aminoamide 446. This is converted in four steps to A -acetyl-L-daunosamine (447), a sugar moiety particularly important as the carbohydrate constituent of the anthracycline antibiotics [149]. 

Key words Phosphopeptide, Monobenzyl protection, Fmoc-based protocol, PEGA, Backbone amide... 

A cinnamoylpiperazine is described as an anti anginal agent. The key intermediate 1 can, in principle, be obtained by alkylation of the monobenzyl derivative of piperazine 71 with ethyl bromoacetate (72). Removal of the protecting group then affords the substituted piperazine (73). Acylation of this with 3,4,5-trimethoxycinamoyl chloride gives cinepazet (74). ... 

The first step of the synthesis of the new ionic liquids 26 involved the selective protection of the OH-3 to give the monobenzyl ether 21 in 56% yield (Scheme 6). Then the exo OH group at position 6 was quantitatively activated as benzenesulfo-nate and treated with an excess of three primary amines in a sealed tube at 160°C to afford the corresponding secondary amino derivatives 23a-C in good yield. The latter compounds were transformed into the tertiary amines 24a-C by reaction with formaldehyde in formic acid (EschweUer-Clark reaction). 

Synthesis of Phosphotyrosine Peptides Using Fmoc-Protected Phosphotyrosine or the Related Monobenzyl Ester... 

Fmoc-Based Solid-Phase Synthesis of Phosphoserine and Phosphothreonine Peptides Using Phosphate Monobenzyl Ester Protection... 

Monomolar benzylation of methyl 2,3-di-0-benzyl-a-D-galactopyranoside in DMF gave 2,3,6-tri-O-benzyl derivative in 73% yield [52], The primary 6-benzyl ether also forms the major part of the monobenzyl fraction obtained from methyl a-D-galactopyranoside or from its p-anomer [53]. Interestingly, position 6 becomes less reactive than position 2 if 3,4-0-isopropylidene acetals is used to protect the other two secondary hydroxyl groups. The ratio of 2- and 6-benzyl ethers was found to be 11 1 in the a-anomer and 2.5 1 in the p-anomer [53] (see also, Ref. [54]). Uridine [55], cyti-dine [56], and 4-(methylthio)uridine [56] also prefer OH-2 over the primary position when benzylated in dimethyl sulfoxide (for other benzylations in this solvent, see Refs. [35, 57]). 

Merrifield resin was reacted with tetrachlorohydroquinone to give a polymeric monobenzyl ether of tetrachlorohydroquinone (77) (0.7mmolg 1 loading). The esters of this functionalized polymer act as polymeric active esters, which have been used for the acylation of amines and the synthesis of some peptides when using the corresponding active esters of N-protected amino acids [95],... 

Further esterification of monobenzyl benzylphosphonate may be carried through the Mitsunobu procedure, the best yields being achieved using the potassium salt of the substrate. Monoesters of iV-protected (1-aminoalkyl)phosphonic acids are further esterified by alcohols in the presence of BOP-type reagents [(l-aminoalkyl)alkylj- and [(l-aminoalkyl)aryl]-phosphinic acids, again as their potassium salts, have been converted into esters by reactive alkyl halides in the presence of 18-crown-6 ether (see also reference The... 

In the presence of a less frequently used base, silver oxide, the introduction of the 0-benzyl protecting group was described in a paper dedicated to the synthesis of a fragment of aplysiatoxins. Contrary to the silent reaction, the sonochemical reaction is reproducible and constitutes, in the authors opinion, the first example of selective monobenzylation of a 1,2-diol at the primary site (Eq. 55). 

NCAs of L-aspartic acid 4-benzyl ester, L-cysteine [869, 870], L-cystine [871, 872], L-tyrosine [873], 4-nitrophenylalanine [874], 1-benzyl-histidine [875], 2,6-diamino-heptanedioic monobenzyl ester [876], L-ornithine, and L-alanine [865] have been prepared from the protected amino acids and PCI5. 

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