Diisopropyl allyloxymethylphosphonate prepared by a one‐pot procedure was isomerized to give racemic 1‐hydroxy‐3‐butenylphosphonate with LDA by a [2,3]‐sigmatropic rearrangement. Chloroacetylation delivered an ester, which was resolved in a two‐phase system by using the lipase from Thermomyces lanuginosus. Racemic and (S)‐α‐hydroxyphosphonate 6 were converted to (±)‐ and (R)‐phosphaaspartic acid by functional‐group manipulation. (±)‐, (R)‐ and (S)‐6 were first esterified with 4‐nitrobenzenesulfonyl chloride before hydroboration to transform the double bond into a hydroxyethyl group. The hydroxyl group was manipulated to give a guanidinyl group and the 4‐nitrobenzenesulfonyloxy to give an amino group. Global deprotection of the α‐aminophosphonates yielded the desired phosphaamino acids.
Reacting ethoxycarbonyl triphenyl phosphorane with activated alkylhalides in chloroform gave the ylides 4 -12. They react smoothly and in general without racemisation with a-amino aldehydes resulting in the dipeptide mimetics 15 -25. Exceptions are the highly labile aldehydes pyridinoalaninal and serinal. Enantiospecificity is proven via enantioselective chromatography.While searching for inhibitors of mast cell activation', it became quite important for us to find an easy and flexible way for producing a-substituted a$-unsaturated y-amino acids, such as 1.During previous work on HIV-Protease inhibitors we gained a lot of experience with BOC-protected a-amino aldehydes in Wittig reactions*. If Wittig-Ylides such as 2 would be easily obtainable, there was a good chance, that the Wittig reaction would be the reaction of choice to obtain an easy access to analogs of 1. 1143
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