5- Alkoxycarbonyl-4-amino

Es kann auch von 4-Alkoxycarbonyl-5-amino-lH-pyrazolen ausgegangen werden ... 

Amino alcohols can be resolved by a number of pathways including hydrolysis, esterification, and transesterification. For example, hydrolysis of Ai,0-diacet5l-2-amino-l-butanol with PPL followed by recrystallization results in (80a) with 95% ee (108). Hydrolysis of racemic acetates or butyrates of 2-[(aLkoxycarbonyl)amino]-l-aLkanols with PFL gives (R)-alcohol (81) with 95% ee (109). (3)-(81) can be obtained by transesterification of the racemic (81) with ethyl acetate which also serves as the reaction medium (109). 

R Amino acid, R NH2 Yield (%) of alkoxycarbonyl-amino acids... 

Finally, cationic ring-opening polymerization of 2-aIkoxy-5(4//)-oxazolones has been used to prepare poly iV-alkoxycarbonyl amino acids. The polymerization was found to be dependent on the nature of the amino acid side chain and the substituent on C-2. 

Activated A-alkoxycarbonyl amino acid derivatives, on the other hand, do not cyclize as readily as A -acyl amino acids, and therefore racemize more slowly. Accordingly, solid-phase peptide synthesis is generally performed by acylation of support-bound amines with activated A -alkoxycarbonyl amino acids. Examples of the preparation of peptides by the inverse strategy (first amino acid linked to the support via its amino group as carbamate activation of support-bound AAacylamino acids) have, nevertheless, been reported [13-16]. 

Reactions of acyclic l-phenylsulfinyl-4-(alkoxycarbonyl)amino butadienes 143 with phenyl vinyl ketone and acrolein were studied by Overman et al. (Scheme 71) [119b]. Good reactivity and complete regioselectivity (controlled by the nitrogen moiety) were the main characteristics exhibited by these dienes. Additionally, the endo approaches are clearly favored with respect to the exo ones (endo/exo ratio is 10 for aldehyde and higher than 100 for ketone). Unfortunately, the 7r-facial selectivity was small or non-existent in both endo and exo approaches, yielding a 1 1 mixture of the two possible diastereoisomers (Scheme 71). 

Methods for Preparing Active Esters of A-Alkoxycarbonyl Amino Acids... 

Discussion of the use of the A(Ai -dicyclohexylcarbodiimide/pentafluorophenol adduct 25 in the preparation of pentaflnorophenyl esters of A-alkoxycarbonyl amino acids can be found in Section 3.2.1.1. 

In the absence of base, active esters of both N-alkoxycarbonyl amino acids and N -protected peptides undergo anninolysis with preservation of chiral integrity. There is ample evidence to substantiate this statementP d and no evidence to the contrary. But there is a wealth of accumulated evidence that active esters undergo isomerization when left in the presence of tertiary annine.t In this regard, 4-nitrophenyl esters are much more sensitive than trichlorophenyl esters and piperidino esters are exceptions in that they are unaffected by tertiary anoine.W The isomerization recently observed in the TBTU-mediated couplings of Fmoc-Cys(R )-OH in the presence of 1,2,3-benzotriazol-l-ol in continuous flow solid-phase synthesis is a further example of this phenomenon. The result can be attributed to the effect of tertiary amine on the benzotriazolyl ester that is formed by capture of the acyluronium intermediate before it has time to be aminolyzed. 

A,A-Bis(alkoxycarbonyl) amino acid fluorides are prepared from the corresponding amino acid derivatives in a manner similar to that described for Boc amino acid fluorides. 

Synthesis of Peptides with AyV-Bis(alkoxycarbonyl) Amino Acid Fluorides... 

Dioxolanesetzensichunter Nitren-Einschiebung mit Azidoameisensaureesler zu 2-Alkoxycarbonyl-amino-1,3-dioxolanen (15 -25%) um198 ... 

Open-chain p-keto esters with an a-amido or a-(alkoxycarbonyl)amino substituents can be hydrogenated with excellent syn-diastereoselectivity [3,41] probably due to conformational lock by a potential hydrogen bond between NH group and the carbonyl oxygen atom of the ester [3]. 

One obvious method for the preparation of NCAs is of course by cyclization of AT-alkoxycarbonyl amino acid chlorides, as originally discovered by Leuchs (eq. 1) (1). Over the years, various improvements of this so-called Leuchs method have been made. While the original procedure used thionylchloride for the chlorination of AT-alkoxycarbonyl a-amino acids, it was foimd that phosphorus bromide is more convenient, allowing cyclization to take place at lower temperatures (4). The rate of cyclization depends on the nature of the alkoxycarbonyl group and decreases in the following order ethyl < methyl < allyl < benzyl. Equation 1 shows a mechanism that is in line with these observations. 

The reactions of 2- and 4-cyanoquinazolines are similar to those of the chloro compounds. Thus the cyano group can be replaced by alkoxide, phenoxide, substituted amino, and hydrazino groups substitution of the 4-cyano takes place more readily than that of the 2-cyano group.The nitrile substituent can also be hydrolyzed to an alkoxycarbonyl and amide group/ ... 

Natriumboranat/Aluminiumchlorid wird hauptsachlich zur selektiven Reduktion von Carbonsaureestern gebraucht, die neben der Alkoxycarbonyl-Gruppe noch eine Carboxy-Gruppe (in Form des Natrium-Salzes), eine unsubstituierte Amino-carbonyl-Gruppe, eine Nitro- oder Halogcn-Gruppe enthalten. 

Komplexbildende Funktionen der Carbonsaure-Komponcntc (Hydroxy-, Amino-, Oxo-Gruppen, stick-stoffhaltige heteroaromatische Ringc), die eine intramolekulare Reduktion der Alkoxycarbonyl-Gruppe ermoglichen4 6. 

Amino-2-alkoxycarbonyl-athyl)- 87 3-(2-Amino-2-alkoxycarbonyl-athyl)-2,3-dihydro-87... 

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