Selective tert‐Butyl Ester Deprotection in the Presence of Acid Labile Protecting Groups with Use of ZnBr₂.

Abstract

Selective tert-Butyl Ester Deprotection in the Presence of Acid Labile Protecting Groups with Use of ZnBr2. -In the presence of ZnBr2, tert-butyl esters containing N-Fmoc or N-Flu protected amino groups can undergo selective deprotection. Methyl esters and allyl esters as well as some other functional groups are not affected under these conditions, but N-Boc and N-trityl groups are cleaved. Interestingly, starting from the diester (Id) selective hydrolysis of the α-tert-butyl ester is possible. -(KAUL, R.; BROUILLETTE, Y.; SAJJADI, Z.; HANSFORD, K. A.; LUBELL*, W. D.; J.

Hydrolysis of esters and dialkyl malonates mediated by t-BuNH2/LiBr/alcohol/H2O

“…On the other hand, as the founding of selective deprotection methods of a particular functional group in the presence of others is still one of the most important transformations in organic synthesis, we decided to test the above reaction conditions for the hydrolysis of an ester group in the presence of a labile amino protecting group such as a carbamate. This selective deprotection is very difficult to carried out and only a few methods are reported (Marcantoni, 2001;Yadav, 2002;Chee, 2001;Bartoli, 2000;Wu, 2000;Kaul, 2004).…”

“…On the other hand, i-propyl, allyl and prenyl esters are less frequently used. For carboxylic acid deprotection a number of useful and reliable procedures are applied (Greene, 1999), including proton (Dhar, 2003) and Lewis (Marcantoni, 2001), acid-or base-catalyzed (Ilankumaran and Verkade, 1999), cleavage, SN2-type dealkylation (Parish and Miles, 1973) and hydrogenolysis (Mandal and McMurray 2007;Pearson, 1999;Jarowicki, 1999;Jarowicki, 2001;Salomon, 1994;Furlán, 1998;Lesutis, 1999;Salmar, 2006;Andrés, 2006;Lee, 2013;Bhattacharya, 2009;Ghosh and Aubé, 2011;Long and Jones, 2011;Koshikari, 2012;Mirgorodskaya, 2012;Hu, 2011;Nakamura, 2011;Ludwig, 2006;Durow, 2006;Yadav, 2002;Chee, 2001; Bartoli, 2000;Wu, 2000;Kaul, 2004;Kabalka, 2001; Andrés and de Rossi 2003;Um, 2007;Poisson, 2005;Morwick, 2006;Liotta, 1981;Li, 2008). Esterases are important biocatalysts that have found wide application in protecting groups chemistry (Kumar and Jolly 1999;Kadereit and Waldmann 2001;Fotakopoulou, 2007;Bordusa 2002).…”

Versatile Triblock Janus Nanoparticles: Synthesis and Self-Assembly

“…Because poly(tert-butyl acrylate) (PtBA) NPs can be functionalized by the hydrolysis of tert-butyl groups under mild conditions, 32 we choose PtBA as the seed NPs. The synthesis of snowman-shaped PtBA−PTMPT JNPs is shown in Figure 1a, with a zeta potential of −54.6 ± 0.9 mV.…”

“…In the triblock JNP synthetic procedures, the PtBA−PTPM JNPs were synthesized in the first step; then the PtBA lobe was hydrolyzed in dichloromethane with ZnBr 2 Lewis acid. 32 The mild hydrolysis conditions will not affect the ester bond in the PTPM lobe but only specifically remove tert-butyl groups from the PtBA lobe. The successful hydrolysis of the PtBA lobe was confirmed by both SEM and FTIR characterizations.…”

Liposomal Formulation of Retinoids Designed for Enzyme Triggered Release

“…The linker moiety tert -butyl 6-hydroxyhexanoate ( 11 ) was coupled with ATRA by a Mitsunobu reaction (Scheme ), which we previously have demonstrated as a reliable method for forming esters of ATRA . The following tert -butyl deprotection led to degradation of the ATRA skeleton under acidic conditions (5% TFA or ZnBr 2 in CH 2 Cl 2 or HF in MeCN), but using 2,6-lutidine and TMSOTf in CH 2 Cl 2 afforded the carboxylic acid 9 in a good yield (Scheme ). The ATRA ester 9 was isolated as yellow crystals and was stable when stored at −20 °C under an inert atmosphere, whereas the oily tert -butyl ester of 9 decomposes upon less than one month of storage.…”