2- Amino-l-phenylethanol

Reaction of Ser-OMe with benzimino ethyl ester resulted in the formation of an oxazoline without racemization (Scheme 27) (85T2379). After forming an amide with 2-amino-l-phenylethanol, Af-phthalimido AAs were oxidized with CrOs and dehydrated by POCI3 to give substituted oxazoles (91JHC1241). 

Ephedrine Ephedrine, L-erythro-l-phenyl-2-methylaminopropanol-l (11.3.4), is synthesized from benzaldehyde in a few different ways. According to the first, benzaldehyde is condensed with nitroethane, giving 2-methyl-2-nitro-l-phenylethanol (11.3.2), which is reduced to 2-methyl-2-amino-l-phenylethanol (11.3.3). The necessary L-isomer is isolated from the mixture of isomers by crystallization. Methylation of this gives ephedrine (11.3.4) [52,53]. 

Much more advanced and effective appeared to be the method reported recently by Beaucage et al. [127]. Starting from ( )-2-amino-l-phenylethanol (88) the authors performed chemoselective N-acylation with ethyl fluoroacetate (89) providing 90, followed by its reaction with hexaethylphosphorous triamide (Scheme 23). Cyclic N-acylphosphoramidite 91 has been obtained as a mixture of diastereomeric rotamers. Condensation of AT4-benzoyl-5 -0-DMT-2 -deoxy-cytidine 92 with 91 in the presence of lH-tetrazole gave, after silica gel chromatography, pure Rc,RP-93 and Sc,SP-93.31P NMR studies indicated that when Rp-93 or Sp-93 was reacted with 3 -0-acetyl-AT-benzoylcytidine (94) and A ATjN jN -tetramethylguanidine (TMG), the dinucleoside phosphotriester was formed in nearly quantitative yield with full P-stereospecificity. After subsequent sulfurization, the P-stereodefined dinucleoside phosphorothioate tri-... 

By the lithium aluminum hydride reduction of amides, amino alcohols (and their derivatives) can be obtained, which have a different arrangement of amino and hydroxy groups to those derived from amino acids. Thus, (5)-2-amino-l-phenylethanol is obtained by reduction of (S)-mandelic acid amide1. 

Second, a nitrile is reduced to a primary amine by hydrogen in the presence of nickel or another transition metal catalyst (Section 18.10C). Catalytic reduction of benzaldehyde cyanohydrin, for example, gives 2-amino-l-phenylethanol. 

The limitations imposed by the thermodynamic relahons due to the reversible nature of the aldol reactions, may be overcome by introducing an ensuing complementary enz3unatic reaction in a cascade fashion. In this way, it is possible to improve the stereochemical outcome of threonine aldolases by selectively transforming one of the diastereosiomers in situ by the action of another enzyme. Toward this end, utilization of L-ThrA in tandem with L-t5u-osine decarboxylase (LTyrDC, PLP-dependent) to produce (I )-2-amino-l-phenylethanol in 89% isolated yield represents a significant example (Scheme 10.28) [194]. 

---