Amino-acid anhydrides

Similarly, A[-carboxy-a-amino acid anhydrides react with aromatics such as toluene, xylenes, and mesitylene to give a-amino acylated products ia moderate yields with almost complete retention of configuration of the a-amino acid. 

The A/-carboxyl group is lost duting the reaction, and no additional deprotection step is requited (104). Benzene reacts with A/-carboxyglyciae anhydride to give aminomethyl phenyl ketone however, it does not react with other A/-carboxy-a-amino acid anhydrides (105). 

Swarc,M. The Kinetics and Mechanism of N-carboxy-a-amino-acid Anhydride (NCA) Polymerization to Poly-amino Acids. Vol. 4, pp. 1—65. 

Trichloromethyl chloroformate has proven effective in the preparation of N-carboxy-a-amino acid anhydrides from amino acids, and various compounds having isocyanate, acid chloride, and chloroformate groups.For example, trichloromethyl chloroformate may be used instead of phosgene in the preparation of 2-tert-butoxycarbonyloxyimino-2-phenylacetonitrile. The use of this reagent is illustrated here by the synthesis of 3-isocyanato-propanoyl chloride from 3-aminopropanoic acid hydrochloride. 

Sekiguchi H (1981) Mechanism of N-carboxy-alpha-amino acid anhydride (Nca) polymerization. Pure Appl Chem 53 1689-1714... 

Knobler Y, Bittner S, Frankel M (1964) Reaction of N-carboxy-alpha-amino-acid anhydrides with hydrochlorides of hydroxylamine O-alkylhydroxylamines + amines syntheses of amino-hydroxamic acids amido-oxy-peptides + alpha-amino-acid amides. J Chem Soc 3941... 

R Katakai, Y Iizuka. An improved rapid method for the synthesis of N-carboxy a-amino acid anhydrides using trichloromethyl chloroformate. (diphosgene). J Org Chem 50, 715, 1985. 

RWilder, S Mobashery. The use of triphosgene in preparation of V-carboxy-a-amino acid anhydrides, (from Boc-amino acids) J Org Chem 57, 2755, 1992. 

When a nonproteinogenic unsaturated amino acid was subjected to the Sharpless asymmetric epoxidation, 49 was formed (87TL3605). It is known that AAs are converted with phosgene into A-carboxy-a-amino acid anhydride (NCA) derivatives. Unexpectedly, A-protected dehydroaspartic acid gave l,3-oxazine-2,6-dione-4-carboxylic acid under such conditions (88CL1473). 

While lactams are often polymerized by anionic ROPs, A-carboxyl-alpha-amino acid anhydrides, called Leuchs anhydrides, can be polymerized by either cationic or anionic techniques (structure 5.29). These polypeptide products, which are called nylon-2 products. 

A wide variety of cyclic monomers have been successfully polymerized by the ring-opening process [Frisch and Reegan, 1969 Ivin and Saegusa, 1984 Saegusa and Goethals, 1977]. This includes cyclic amines, sulfides, olefins, cyclotriphosphazenes, and IV-carboxy-oc-amino acid anhydrides, in addition to those classes of monomers mentioned above. The ease of polymerization of a cyclic monomer depends on both thermodynamic and kinetic factors as previously discussed in Sec. 2-5. 

A-Carboxy-a-amino acid anhydrides, also referred to as 4-substituted oxazolidine-2,5-diones, Leuchs s anhydrides, or N-carboxyanhydrides (NCA), are polymerized by bases and transition metal complexes. Polymerization proceeds with simultaneous decarboxylation to produce a polyamide... 

For copolymerizations proceeding by the activated monomer mechanism (e.g., cyclic ethers, lactams, /V-carboxy-a-amino acid anhydrides), the actual monomers are the activated monomers. The concentrations of the two activated monomers (e.g., the lactam anions in anionic lactam copolymerization) may be different from the comonomer feed. Calculations of monomer reactivity ratios using the feed composition will then be incorrect. 

Copolymerizations between pairs of cyclic esters, acetals, sulfides, siloxanes, alkenes, lactams, lactones, /V-carboxy-a-amino acid anhydrides, imines, and other cyclic monomers... 

Bamford, C. H. andH. Block, The Polymerization of Af-Carboxy-a-Amino Acid Anhydrides, Chap. 8 in Comprehensive Chemical Kinetics, Vol. 15, C. H. Bamford and C. F. H. Tipper, eds., Elsevier, New York, 1976. 

Shalitin, Y., A-Carboxy-a-Amino Acid Anhydrides, Chap. 10 in Ring-Opening Polymerization, K. C. Frisch and S. L. Reegen, eds., Marcel Dekker, New York, 1969. 

The stereochemistry of ring-opening polymerizations of episulfides, lactones, lactides, IV-carboxy-a-amino acid anhydrides, and other monomers has been studied but not as extensively as the epoxides [Boucard et al., 2001 Chatani et al., 1979 Duda and Penczek, 2001 Elias et al., 1975 Guerin et al., 1980 Hall and Padias, 2003 Imanishi and Hashimoto, 1979 Inoue, 1976 Ovitt and Coates, 2000 Spassky et al., 1978 Zhang et al., 1990]. 

Avery interesting method of synthesis of polypeptides from N-carboxy-a-amino acid anhydrides was proposed by Ballard and Bamford. Opening the ring of N-carboxy-a-amino acid anhydrides by primary or secondary amines can be illustrated by the following reaction ... 

Ring-opening copolymerization was simultaneously investigated with homopolymerization of N-carboxy-a-amino acid anhydrides, NCAs, by Bamford at al Polymerization of a mixture of NCAs of y-ethyl-L-glutamate and sarcosine ... 

The only example of kinetic considerations dealing with the ring-opening polymerization was published by Ballard and Bamford. The authors examined polymerization of N-carboxy-amino acid anhydrides proceeding onto polysacrosine. The authors assumed the equilibrium between adsorbed molecules of monomer, E, and free monomer, M, described by equilibrium constant, K, independent of the position in the template chain ... 

Anionic Polymerization. Anionic grafting polymerization initiated on the inorganic particles is also possible to give composite particles. The amino group incorporated into the surface of silica caused anionic polymerization of N-carboxy-a-amino acid anhydride to give poly(amino acid) grafting [Reaction (8)1 (21). 

Several 3-alkylidenepiperazine-2,5-diones have been prepared by a novel route involving the prior coupling of a /-butoxycarbonyl amino acid with an N-carboxydehydro amino acid anhydride, followed by removal of the protecting group (87H2087) (Scheme 6). 

---