Diastereoselective Alkylation of Schiff Bases for the Synthesis of Lipidic Unnatural Fmoc-Protected α-Amino Acids

New GM1 Ganglioside Derivatives for Selective Single and Double Labelling of the Natural Glycosphingolipid Skeleton

“…HClO 4 (70 %). tert ‐Butyl 2‐aminostearate ( 4 ‐ t BuO,NH 2 )33 was synthesized from 4 ‐OH,NH 2 · HCl, which could be obtained either from 2‐bromostearic acid ( 4 ‐OH,Br)30 via the azide 4 ‐OH,N 3 34 (to avoid treatment of 4 ‐OH,Br with ammonia in an autoclave35) or by saponification of the methyl ester 4 ‐MeO,NH 2 · HCl 36. The choice and further use either of methyl or of tert ‐butyl 2‐aminostearate depends on the compatibility of a given fluorophore with basic or acidic conditions required for the deprotection of the carboxy group.…”

“…The synthesis of the NHS ester of the Fmoc‐protected α‐aminostearic acid 4 ‐NHS,NHFmoc is shown in Scheme . Compound 4 ‐ t BuO,NH 2 was treated with FmocCl in dioxane, the α‐carboxy group was then deprotected with TFA in CH 2 Cl 2 ,33 and the acid 4 ‐OH,NHFmoc was activated with bis( N ‐succinimidyl) carbonate to yield the desired active ester 4 ‐NHS,NHFmoc.…”

Tandem Ru‐alkylidene‐catalysed cross metathesis/hydrogenation: synthesis of lipophilic amino acids

“…The requirement for chromatography to separate the resultant Schiff base isomers, however, is not trivial and also unsuitable for large‐scale synthesis. An asymmetric synthesis of LAAs ( n = 11, 13 and 15) has also been reported using a diastereoselective alkylation of the Schiff base of 2‐hydroxypinan‐3‐one and tert ‐butyl glycinate (Scheme ) . Although the observed diastereoselectivity is excellent (>90% de), the alkylation yields are low and require the more expensive (+)‐isomer of the α ‐pinene derivative to access l ‐configured LAAs.…”