Base-labile

H2O2, (NH4)6Mo7024 NaOH, pH 11, 97% yield. The MTM ester is converted to the much-more-base labile methylsulfonylmethyl ester. It is possible to hydrolyze the methylsulfonylmethyl ester in the presence of the MTM ester. 

This ester was designed as a base-labile protective group. Monoprotection of aspartic acid was achieved using the DCC/DMAP protocol. Cleavage is... 

Few methods exist for the protection of sulfonic acids. Imidazolides and phenolic esters are too base labile to be useful in most cases. Simple sulfonate esters often cannot be used because these are obviously quite susceptible to nucleophilic reagents. 

The Bnpeoc group was developed as a base-labile protective group for solid-phase peptide synthesis. The carbamate is formed from the O-succinimide (DMF, 10% Na2C03 or 5% NaHC03) and is cleaved using DBN, DBU, DBU/AcOH, or piperidine. ... 

The Dnseoc group was developed as a base-labile protective group for the 5 -hydroxyl in oligonucleotide synthesis. It is cleaved with DBU in aprotic solvents. The condensation of oligonucleotide synthesis can be monitored by UV detection at 350 nm or by fluorescence at 530 nm of the liberated vinylsulfone. ... 

At this stage of the synthesis, it was convenient to protect the secondary amino function in 56 as the base-labile FMOC derivative22 through the use of the corresponding chloroformate (96% yield). In the planning phase, the selection of an FMOC protecting... 

Vinyl sulfones such as 262 are smoothly converted to a,) -unsaturated nitriles such as 263 on treatment with KCN in the presence of dicyclohexyl-18-crown-6 in refluxing t-butyl alcohol (equation 155)148. The reaction conditions are compatible with base-labile functionalities such as a methoxycarbonyl group (equation 156)148. This method can be used in the preparation of the sesquiterpene aldehyde nuciferal from allyl phenyl sulfones. 

In the Fmoc protection approach, the acid-labile ferf-butyl groups are often used for side-chain protection. The base-labile Fmoc groups can be easily removed during a synthesis using piperidine (Fig. 4). The final global deprotection together with cleavage from the polymeric support is achieved with TFA. 

A variety of cleavage conditions have been reported for the release of amines from a solid support. Triazene linker 52 prepared from Merrifield resin in three steps was used for the solid-phase synthesis of aliphatic amines (Scheme 22) [61]. The triazenes were stable to basic conditions and the amino products were released in high yields upon treatment with mild acids. Alternatively, base labile linker 53 synthesized from a-bromo-p-toluic acid in two steps was used to anchor amino functions (Scheme 23) [62]. Cleavage was accomplished by oxidation of the thioether to the sulfone with m-chloroperbenzoic acid followed by 13-elimination with a 10% solution of NH4OH in 2,2,2-trifluoroethanol. A linker based on l-(4,4 -dimethyl-2,6-dioxocyclohexylidene)ethyl (Dde) primary amine protecting group was developed for attaching amino functions (Scheme 24) [65]. Linker 54 was stable to both acidic and basic conditions and the final products were cleaved from the resin by treatment with hydrazine or transamination with ra-propylamine. 

Garcia-Echeverria C. A base labile handle for solid phase chemistry. Tetrahedron Lett 1997 38 8933-8934. 

Veerman JJN, Rutjes FPJT, Van Maarseveen JH, Hiemstra H. A novel acid stable/base labile carbamate linker for N-acyliminium ion reactions on solid support. Tetrahedron Lett 1999 40 6079-6082. 

The cycloreversion experiments showed a clean Tf=T-DNA to T/T-DNA transformation. No by-products were detected, which supports the idea that DNA may be more stable towards reduction compared to oxidation. Even heating the irradiated DNA with piperidine furnished no other DNA strands other then the repaired strands, showing that base labile sites - indicative for DNA damage - are not formed in the reductive regime. The quantum yield of the intra-DNA repair reaction was therefore calculated based on the assumption that the irradiation of the flavin-Tf=T-DNA strands induces a clean intramolecular excess electron transfer driven cycloreversion. The quantum yield was found to be around 0=0.005, which is high for a photoreaction in DNA. A first insight into how DNA is able to mediate the excess electron transfer was gained with the double strands 11 and 12 in which an additional A T base pair compared to 7 and 8 separates the dimer and the flavin unit. 

Bemdl S, Herzig N, Kele P et al (2009) Comparison of a nucleosidic vs non-nucleosidic postsynthetic click modification of DNA with base-labile fluorescent probes. Bioconjug... 

De Visser PC, van Helden M, Filippov DV, van der Marel GA, Drijfhout JW, van Boom JH, Noort D, Overkleeft HS (2003) A novel, Base-Labile Fluorous Amine Protecting Group Synthesis and Use as a Tag in the Purification of Synthetic Peptides. Tetrahedron Lett 44 9013-9016... 

The synthesis of lipidated peptides is implicated by the base-lability of the thioester and the acid sensitivity of the prenyl group double bonds. Thus, new protecting groups are required which can be removed under extremely mild, preferably neutral, conditions. 

In the course of the enzymatic reactions (Scheme 8) neither the C-terminal methyl ester nor the base labile thioester was effected.1111... 

The selectivity and mildness of the Pd(0)-catalyzed deprotection of allyl (All) esters and the allyloxycarbonyl (Aloe) urethanes117 181 reaction also allowed for the successful and efficient application of this blocking group technology in the synthesis of acid- and base-labile lipidated pepti-... 

It has long been recognized that polymeric supports for oligosaccharide synthesis do not need to be insoluble.33 Wang et al. applied the sulfoxide glycosylation method to the synthesis of disaccharide 79 (Scheme 3.14). The key feature of this work was the base-labile linker. Sulfoxide 74 was used to glycosylate polyethylene glycol... 

The base lability of succinoyl diester hnker severely limits the selection of protecting groups available for an oligosaccharide synthesis, so a more versatile tether was required. Diether bonds of benzylphenol or dibenzyl of 1,4-di(hydroxymethyl)-benzene satisfy this requirement because they are stable to both bases and to acids. A sufficient acid stability is important since the formation of a glycosidic bond is an acid-catalyzed reaction, not surprisingly, as it is an acetal functionality. For instance, DOX,34 the dibenzyl hnker a,a -DiOxyXylyl diether, -0CH2C6H4CH20-, is not limited by restriction of the succinoyl hnker (1) when bound via a hydroxyl or as an... 

CGJ Verhardt, GI Tesser. New base-labile amino-protecting groups for peptide synthesis. Rec Trav Chim Pays-Bas 107, 621, 1988. 

VV Samukov, AN Sabirov, PI Pozdnyakov. 2-(4-Nitrophenyl)sulfonylethoxycarbonyl (Nsc) group as a base-labile a-amino protection for solid phase peptide synthesis. Tetrahedron Lett 35, 7821, 1994. 

The group of allyl-based linkers was developed by Kunz et al. [49] Linkers of the general allyl type are particularly valuable, because they are removable under almost neutral conditions using palladium catalysis and are orthogonally stable towards the commonly used acid and base-labile protecting groups (Tab. 3.2). 

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