Amino acids, acetylenic

An unknown acetylenic amino acid obtained from the seed of a tropical fruit has the molecular formula C7H11NO2. On catalytic hydrogenation over platinum this amino acid yielded homoleucine (an amino acid of known structure shown here) as the only product. What is the structure of the unknown amino acid ... 

Pharmacologically active allenic steroids have already been examined intensively for about 30 years [5], Thus, the only naturally occurring allenic steroid 107 had been synthesized 3 years before its isolation from Callyspongia diffusa and it had been identified as an inhibitor of the sterol biosynthesis of the silkworm Bombyx mori (Scheme 18.34) [86d], At this early stage, allenic 3-oxo-5,10-secosteroids of type 108 were also used for the irreversible inhibition of ketosteroid isomerases in bacteria, assuming that their activity is probably caused by Michael addition of a nucleophilic amino acid side chain of the enzyme at the 5-position of the steroid [103, 104]. Since this activity is also observed in the corresponding /3,y-acetylenic ketones, it can be rationalized that the latter are converted in vivo into the allenic steroids 108 by enzymatic isomerization [104, 105],... 

The oxidation of propargyl alcohol to the acid and of but-2-yne-l,4-diol to acetylene dicarboxylic acid is carried out on a technical scale at a lead dioxide anode in sulphuric acid [4, 5]. Electrochemical oxidation of acetylenic secondary alcohols to the ketone at lead dioxide in aqueous sulphuric acid [4], gives better results than the cliromic acid based process of Jones [6], Oxidation of aminoalkan-1-ols to the amino acid at a lead dioxide anode in sulphuric acid is achieved in 31 -73 % 5delds [7]. This route is applied to the technical scale production of (l-alanine from 3-aminopropanol in an undivided cell [8]. 

Despite the uncertainties regarding regiochemistry, the reaction of propiolates with miinchnones has found use in synthesis. Kane and co-workers (84) synthesized the calcium channel activator FPL 64176 (161) using a mtinchnone cycloaddition protocol. Thus, reaction of amino acid 158 with acetic anhydride in the presence of acetylenic dipolarophUe 159 gave pyrrole 160 in 49% yield. Base-induced elimination of the 4-nitrophenethyl protecting group afforded FPL 64176 (161) in 85% yield. 

Amino acids in general Crown ether and open chain polymer of transtetra-hydro furan, 2,5-bis acetylene unit SLM Highly selective separation and enantiomeric resolution [98,99]... 

The carbon skeleton of the unknown acetylenic amino acid must be the same as that of homoleucine. The structure of homoleucine is such that there is only one possible location for a carbon-carbon triple bond in an acetylenic precursor. 

For the synthesis of optically pure building blocks we mainly focused on the synthesis of protected noncoded (R)- and (S)-amino acids, as they can be synthesized reliably in enantiomerically pure form with a large variety of side chains using asymmetric hydrogenation of a-amino-a, 3-didehydroamino acids using cationic diphosphine rhodium catalysts.216,217 As a typical example of a reactophore we present a-alkynyl ketones, which is a representative bis-acceptor molecule. In Scheme 5 are depicted some of the many synthetic applications of acetylenic ketones in heterocyclic synthesis, which have great potential for combinatorial and parallel organic synthesis. 

M. C. Sharma, A. K. Garcia, J. M. Gonzalez, A. Landa, C. Linden, A. a-Oxymethyl ketone enolates for the asymmetric Mannich reaction. From acetylene and N-alkoxycarbonylimines to /J-amino acids. Angew. Chem. Int. Ed. 2000, 39, 1063-1065. 

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