218800-38-5Relevant articles and documents
Preparation of the β2-homoselenocysteine derivatives Fmoc-(S)-β2hSec(PMB)-OH and Boc-(S)-β2hSec(PMB)- OH for solution and solid-phase peptide synthesis
Patora-Komisarska, Krystyna,Jadwiga Podwysocka, Dominika,Seebach, Dieter
scheme or table, p. 1 - 17 (2011/03/17)
Fmoc-β2hSer(tBu)-OH was converted to Fmoc-β2hSec(PMB)-OH in five steps. To avoid elimination of HSeR, the selenyl group was introduced in the second last step (Fmoc- β2hSer(Ts)-OAll→Fmoc-β2hSec(PMB)-OAll). In a similar way, the N-Boc-protected compound was prepared. With the β2hSe-derivatives, 21 β2-amino-acid building blocks with proteinogenic side chains are now available for peptide synthesis. Copyright
A useful modification of the Evans auxiliary: 4-Isopropyl-5,5- diphenyloxazolidin-2-one
Hintermann, Tobias,Seebach, Dieter
, p. 2093 - 2126 (2007/10/03)
The 4-isopropyl-5,5-diphenyloxazolidinone (1) is readily prepared from (R)- or (S)-valine ester, PhMgBr, and ethyl chlorocarbonate. It has a melting point of ca. 250°, a low solubility in most organic solvents, and a C=O group which is sterically protected from nucleophilic attack. Thus, the soluble N-acyl-oxazolidinones (7-16) can be prepared from 1 with BuLi at temperatures around 0°instead of - 78°(Scheme 3), their Li enolates can be generated with BuLi, rather than with LDA, and deacylation in the final step of the procedure can be achieved with NaOH at ambient temperatures (Scheme 12), with facile recovery of the precipitating auxiliary 1 (filtering, washing, and drying). The following reactions of N-acyl-oxazolidinones from 1 have been investigated: alkylations (Scheme 4), aminomethylations and hydroxymethylations (Scheme 5), aldol additions (Schemes 6 and 7), Michael additions (Schemes 9 and 10), and a (4 + 2) cycloaddition (Scheme 11). The well-known features of reactions following the Evans methodology (yield, diastereoselectivity, dependence on conditions, counter ions, additives etc.) prevail in these transformations. Most products, however, have higher melting points and a much more pronounced crystallization tendency than those derived from conventional oxazolidinones, and can thus be purified by recrystallization, avoiding chromatography (Table 1). The disadvantage of 1 having a higher molecular weight (ca. 150 Da) than the non-phenyl-substituted auxiliary is more than compensated by the ease of its application, especially on large scale. A number of crystal structures of oxazolidinones derived from 1 and a TiCl4 complex of an oxazolidinone are described and discussed in view of the diastereoselective-reaction mechanisms.