Deprotection methods

Although use of automated oligonucleotide synthesis is widespread, work continues on the optimization of protecting groups, coupling conditions, and deprotection methods, as well as on the automated devices.56... 

Microwave-assisted epoxide ring-openings of l,5 2,3-dianhydro-4,6-0-benzyl-idene-D-allitol with nucleobases have been reported [218], Various rapid microwave-assisted protection and deprotection methods in the area of carbohydrate chemistry are known [210], and two general review articles on microwave-assisted carbohydrate chemistry were published in 2004 [219, 220]. 

Allylic amination is important for the solid-phase organic synthesis.15 The solid-phase allylic aminations are devised into the G-N bond formation on solid support and the deprotection of allyl ethers. As a novel deprotection method, the palladium-catalyzed cyclization-cleavage strategy was reported by Brown et al. (Equation (4)).15a,15b The solid-phase synthesis of several pyrrolidines 70 was achieved by using palladium-catalyzed nucleophilic cleavage of allylic linkages of 69. 

An alio-threonine analogue was prepared in this way. The Nebraska group has also explored the use of diallyl phosphonates driven by the need to develop mild deprotection methods [77]. Treatment of ketophosphonates with alkoxide base led to the formation of difluoroenolates and thus difluoromethylketones [78]. The lithiophosphate then acts as a synthetic equivalent for the difluoro-methyl anion synthon (Eq. 21). 

Ley, S.V. and Mynett, D.M., Microwave promoted hydrolysis of esters absorbed on alumina a new deprotection method for pivaloyl groups, Synlett, 1993, 793. 

An alternative deprotection method, which proceeds without prior isomerisation, involves heating under reflux the allyl ether in aqueous methanol with palladium/activated charcoal in the presence of toluene-p-sulphonic acid.79... 

Denkewalter et al. [90] reported the synthesis of monodendron polyamides through generation 10. The scheme involved protection/deprotection methods commonly used by polypeptide chemists. Dendron construction started with benzhydrylamine as the initiator core and an activated ester of amino-protected L-lysine as the branching reagent (Scheme 4). 

The use of protection/deprotection methods or highly differentiated, branch cell reagents allows selective coupling without bridging or looping side reactions. Table 4 summarizes just a few of the branch reagents used successfully so far. 

The second part deals with the grafting of amines or alcohols with protection/ deprotection methods and the third one presents the grafting of alkenes bearing free hydroxyl or acid functions. Finally, a table summarizing all experiments is also presented. 

It is possible to obtain diversity in the solid phase synthesis of lamellarins by modifying the conditions of cleavage <04T0000>. The selection of different Lewis acids as a cleavage/deprotection method in the solid-phase synthesis of 147 can produce several analogues, which, after purification, can be submitted for biological evaluation. 

A protected eglin c was synthesized by the minimum protection strategy. 1 Of the several deprotection methods available, eglin c was obtained using the HF procedure. 

Total deprotection with tris(dimethylamino)sulfonium difluoro-trimethylsilicate (TAS-F, (Me2N)3S F2SiMe3 ) afforded the target molecule 4 in 70 % yield. This mild deprotection method is especially useful when dealing with base- or acid-sensitive compounds. 

It is known that pyridinium tribromide converts olefins with specific r/7 t/-dibromina-tion. Therefore, the v/c-dibromides thus obtained can be cathodically reduced to the original olefins without geometrical changes of molecular structure [218]. This stereospecific bromination-debromination may be useful as an olefin protection-deprotection method. 

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