0-Acetyllactic acid

An alternative employs classical resolution using lactic acid as the source of asymmetry. Amide formation from (S)-O-acetyllactic acid and 13 gave a separable mixture of 14 [14, 15]. The lactanilides could be eliminated or reduced [16] to remove the stereogenic centre to give optically active analogues of 9 and 11. Nonetheless, a serious problem with the effective use of anilides as auxiliaries is their recovery in enantiomerically pure form. 

The conclusion was reached that the biosynthetic route was by way of a two-carbon insertion into 2-oxo-3-hydroxy-3-methylbutyric acid (CLXXIV). Taken in conjunction with the established bios3uithesis of valine (CLXXV) from pyruvic acid by way of acetyllactic acid (CLXXVI) and the ketol rearrangement to CLXXIV the biosynthesis of echimidinic acid may be formulated as in Chart VI. 

Acetyllactic acid results from an acyloin condensation and loss of carbon dioxide, followed by a very interesting ketol rearrangement, which proceeds in a stereochemically uniform manner. Herein, the hydroxy- and keto-groups are oriented syn-periplanar, so that the methyl group is transferred suprafacially on the (Jle)-side, a mechanism, which is supported by data from NMR spectroscopy on model compounds [260] and by preparative examples. [261, 262] The ketol rearrangement is to some extent related to the benzil-benzilic acid rearrangement. 

S-Acetoxypropionic acid 2-Hydroxypropanoic acid acetate Acetyllactic acid... 

The values chosen were either those obtained without a solvent or those with the highest concentration of solute. The differences calculated in columns 5 and 8 were obtained by using the rotations of the esters of acetylalanine and acetyllactic acid as a basis. 

The reduction of hepta-O-acetyl-a-lactosyl bromide with zinc and acetic acid produces hexa-O-acetyllactal which, on deacetylation with am-... 

Ozonolysis of hexa-O-acetyllactal gives 3-0- -D-galactopyranosyl-D-arabinose hexaacetate. Hydroxylation of lactal with aqueous peroxy-benzoic acid led to the isolation of only one isomer, namely 4-0- -d-galactopyranosyl-D-mannose (53), although Watters and Hudson later... 

Various 2-furanone chiral building blocks are readily accessible from 0-acetyllactate derivative 222 according to the series of reactions outlined in Scheme 37. Deprotonation of 222 with 2-4 equivalents of LiHMDS gives (/S)-7-methyltetronic acid (257) in nearly quantitative yield [88]. Reduction of 257 with ammonia—borane affords a 25 75 mixture of 258 and 259, whereas catalytic hydrogenation over rhodium/carbon produces an 85 15 mixture of 258 and 259 [89]. Dehydration of the mixture with phosphorus oxychloride furnishes the 55 -butenolide 260 [(+ )-angelica lactone]. Dihydrofiiranone 262 is made by benzoylation of the tetrabutylammonium salt of 257 followed by catalytic hydrogenation. 

Like the above rhodium complexes of S,S-chiraphos, this R-prophos rhodium complex is an efficient homogeneous catalyst for the production of a-amino acids, and the optical yields appear to be insensitive to the nature of the substituents on the substrates which provide the naturaf 5 -amino acids in 90 3% optical yields and high chemical yields (<87%) [compare with the S,S-chiraphos rhodium precatalysts above which gives the non-natural R- a-amino acids]. Furthermore, the catalyst R-prophos rhodium complex can breed its own chirality so that large quantities of 7 -prophos can be made from the catalytic hydrogenation of ethyl acetoxyaciylate, via ethyl S-(9-0-acetyllactate, by the 7 -prophos catalyst itself This procedure has been used to produce S-prophos... 

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