Serine tert.butyl ether

In peptide synthesis functional groups in the amino acid side chains are often protected with acid-labile protecting groups (Section 4.5.3). The tripeptide in Figure 4.35 contains, for example, a serine ferf-butyl ether and an L-lysine e-protected as an O-tert-butyl carbamate. In the standard strategy of synthesizing oligopeptides from the C- to the N-terminus (cf. Section 6.4.3) the C-terminus is either connected to the acid-labile... 

The tert-butyl ethers of serine and threonine are available by tert-butylation of various starting materials, e.g. Z-Ser-OMe/Z-Thr-OMe,P l Z-Ser-ONbz/Z-Thr-ONbz,P l and H-Ser-OMe TosOH/H-Thr-OMe -TosOHt l (see also Table 3). Analogous to benzyl ether formation, the tert-butyl ethers can also be produced via 4-substituted 2,2-difluoro-l,3,2-ox-azaborolidin-5-ones.t In most cases, isobutylene with 4-toluenesulfonic add, or a concentrated inorganic acid is used as catalyst for tert-butylation. The use of Fmoc-Ser(tBu)-OH and Fmoc-Thr(tBu)-OH in solid-phase peptide synthesis is very well established. These annino acid derivatives can be synthesized either by introduction of the Fmoc group into H-Ser(tBu)-OH and H-Thr(tBu)-OH or by tert-butylation of the Fmoc-protected serine and threonine (Table 3). ... 

An important alternative for the benzyl group is the tert.butyl group. The tert.butyl ethers of serine, threonine and tyrosine... 

With a view to the preparation of asymmetric tra s-oc-(2-phenylcyclopropyl)glycines from L-serine, the latter was first converted to the chiral derivative, tert-butyl (EAR )-2,2-dimethyl-4-(2-phenylvinyl)oxazolidine-3-carboxylate and this was then subjected to cyclopropanation with diethylzinc/diiodomethane in diethyl ether at reflux temperature.89 The resulting cyclopropane derivatives were obtained as a 25 75 mixture of diastereomers in 50% yield that could not be resolved, hence the sequence was not continued to the target compounds. 

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