3/28/2023 0 Comments Boc anhydride![]() 5 In connection with attempts to convert lactams to ω-amino acids, Grieco et al. 3 Synthetic background Di- tert-butyl dicarbonate or tert-butyl pyrocarbonate, Boc 2O, is an excellent reagent for the preparation of all sorts of Boc-derivatives. ![]() The very large number of amino acid and peptide derivatives initially referred to belong to the subgroups on line 2, whereas many of the compounds with bis-protected amino functions discussed below are included among them in column 2 on the last line. The figures further demonstrate that most of these substances, over 65%, are Boc-derivatives and that the majority contain one substituent in addition to hydrogen. Presently, over 7.2 × 10 7 organic and inorganic compounds are described in the CAS® registry and as can be seen from Table 1 nearly 0.7% contain one of the three protecting groups mentioned. To put things in a proper perspective, for comparison the corresponding figures for Cbz and Fmoc are also included.Ī GH any group. This is illustrated in Table 1, in which figures on the occurrence of various classes of Boc-compounds, Boc- N-(GH) 2 and Boc- N-G 2, collected from Reaxys® are presented. 2 Statistic perspectives In addition to providing access to relevant previous work in the chemical literature, modern computerized chemical data banks can furnish surveys of related information available, otherwise difficult to foresee, search for or collect. To the best of our knowledge this is the first review dealing with these topics. The synthetic aspects leading to such compounds and the properties and applications of them are discussed in this paper. 4 Other NH-compounds including various protected/acylated amines have also been substituted in this way that thereby give rise to bis-protected amino functions. 3 More recently the preferences have changed and nowadays Boc is ranked as “one of the most commonly used protective groups for amines”. In retrospect it seems that outside the peptide field the break-through in the use of Boc came a bit later as judged from the first monographs devoted to protecting groups. It was also applied nearly from the outset of solid phase peptide synthesis for temporary protection of the α-amino group and continues to play an important role in this context in parallel with the Fmoc-group (Fmoc = 9-fluorenylmethyloxycarbonyl). 2 Besides, within a few years Boc-amino acids became commercially available which contributed to the fast success of this protecting group. ![]() These and other developments and aspects related to Boc-protection in peptide synthesis have already been comprehensively documented. Initially the preparation of Boc-amino acids was a bit cumbersome but gradually better reagents and methods became available. Instead Boc can be cleaved by mild acidolysis, whereas benzyl carbamates require significantly stronger acidic conditions for their deprotection. In that context Boc-derivatives nicely complemented the corresponding, then relatively novel, benzyl carbamates (Cbz-compounds) which could be deprotected by catalytic hydrogenolysis or sodium in liquid ammonia, conditions under which Boc is completely stable. Boc-protection 1 was introduced in the late fifties and was rapidly applied in the field of peptide synthesis. 1 Introduction When in a synthetic project there is a need to protect an amino function, its conversion to tert-butyl carbamate is nowadays generally the first option, because of the attractive properties of the resulting so-called Boc-derivative. Attention is directed towards cases of facilitated cleavage due to mutual interaction between two protecting groups on the same nitrogen. This review highlights various aspects related to the synthesis, properties and applications of products containing one or two Boc-groups resulting from dual protection of amines and amides. Primary amines are unique because they can accommodate two such groups. Protecting groups play a pivotal role in the synthesis of multifunctional targets and as amino functions often occur in this context, issues related to their protection become prominent.
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