Amino acid unusual

Several L-amino acids have physiological functions as free 

Homocysteine, homoserine, ornithine, and citrulline are intermediates in the biosynthesis of certain other amino acids. 

Taurine, which has an amino group in the 6-carbon and a sulfonic acid group instead of COOH, is present in the CNS and as a component of certain bile acids participates in digestion and absorption of lipids in the gastrointestinal tract. 

Hypoglycin A is present in unripe akee fruit and produces severe hypoglycemia when ingested. 

Some D-amino acids are found in polypeptide antibiotics, such as gramicidins and bacitracins, and in bacterial cell wall peptides. 

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Analysis of carbon compounds—even amino acids—from extraterrestrial sources might provide deeper insights into this mystery. John Cronin and Sandra Pizzarello have examined the enantiomeric distribution of unusual amino acids obtained from the Murchison meteorite, which struck the earth on September 28, 1969, near Murchison, Australia. (By selecting unusual amino... 

Barton and co workers have explored the aryladon of various nucleophiles inclndmg nitroalkanes using bismuth reagents Reacdon of 2-nitropropane v/ith triphenylbismnth carbonate gives 2-nitro-2-phenylpropane in 80% yield Recently, this aryladon has been used for the synthesis of unusual amino acids Aryladon of ct-nitro esters v/ith triphenylbismnth dichloride followed by redncdon gives unique ct-amino acids fEq 5 68 ... 

Some Peptides Contain Unusual Amino Acids... 

Vitamin K is the cofactor for the carboxylation of glutamate residues in the post-synthetic modification of proteins to form the unusual amino acid y-carboxygluta-mate (Gla), which chelates the calcium ion. Initially, vitamin K hydroquinone is oxidized to the epoxide (Figure 45-8), which activates a glutamate residue in the protein substrate to a carbanion, that reacts non-enzymically with carbon dioxide to form y-carboxyglut-amate. Vitamin K epoxide is reduced to the quinone by a warfarin-sensitive reductase, and the quinone is reduced to the active hydroquinone by either the same warfarin-sensitive reductase or a warfarin-insensitive... 

Although it is toxic in large doses, selenium is an essential micronutrient in all known forms of life. It is a component of the unusual amino acids selenocys-teine and selenomethionine. In humans, selenium is a trace element nutrient. 

The anion derived from ethyl 2-nitropropionate reacts with various reductive alkylating agents (S l substrates) to give new unsymmetrically disubstitutednitro esters (Eq. 5.35), which are interesting precursors for unusual amino acids.53... 

X,P-Dehydro-a-amino acids are prepared by elimination of HN02 from P-nitro-a-amino acids, which are prepared by reaction of a-bromoglycine derivatives with alkyl nitronates (see Eq. 7.135).181 This process is a new type of the Michael addition of nitro compounds followed by elimination of HNOz. Such unusual amino acids are interesting as enzyme inhibitors.182... 

Advanced ChemTech is a Peptidology Company offering synthesis of peptides, peptoids and unusual amino acids to its customers. Advanced ChemTech is a CreoSalus company. 

Dihydroxypyridazines are readily prepared from the diene 103 and DEAZD or PTAD,159 and the amino acid 104, a constituent of the Monamycin antibiotics, was synthesized from the Diels-Alder adduct of phthalazine-l,4-dione and penta-2,4-dienoic acid.160 These unusual amino acids can also be synthesized from the PTAD and parent HTAD adducts of penta-2,4-dienoic acid,161 and a variety of similar adducts, triazolo-pyridazines 105, has been synthesized from a wide range of 4-substituted 1,2,4-triazole-3,5-diones.162... 

The same behavior toward butadiene derivatives is documented for several bicyclic and polycyclic diazaquinones. Phthalazinedione 83a when treated with a wide variety of dienes afforded adducts 95 (60JOCI724 62JA966, 62JOC1115 70BCJ3926 75MI3 76H135). The unusual amino acid derivative 96 was prepared in a similar fashion (Scheme 23) (91CZ292). 

A similar reaction of 1 with the bromo acetal S also proceeds with retention to provide 6, a useful precursor to unusual amino acids. 

Wootton, J. C. (1994). Sequences with unusual amino-acid compositions. Curr. Opin. Struct. Biol. 4, 413-421. 

The prion domains of Ure2p, Sup35p, and Rnqlp have unusual amino acid compositions, with abnormally high contents of the polar uncharged residues, Asn and Gin, and relatively low contents of charged and hydrophobic amino acids. In contrast, the amino acid composition of the HET-s prion domain is more typical of a normal globular protein. 

The many (possibly more than 30) types of collagens found in human connective tissues have substantially the same chemical structure consisting mainly of glycine with smaller amounts of proline and some lysine and alanine. In addition, there are two unusual amino acids, hydroxyproline and hydroxylysine, neither of which has a corresponding base-triplet or codon within the genetic code. There is therefore, extensive post-translational modification of the protein by hydroxylation and also by glycosylation reactions. 

The unusual amino acid (S)-2-amino-(Z)-3,5-hexadienoic acid (269), which is a component of the toxic y-glutamyl dipeptide isolated from the defensive glands of the Colorado beetle [209], has been synthesized along Scheme 17, after two initial attempts had proved unsuccessful due to the instability of 269 towards various oxidation conditions [210]. Scheme 17 relies on the hydrolysis of an ortho ester to generate the required carboxylic acid. Thus, the L-serine aldehyde equivalent 270 was treated with ( )-l-trimethylsilyl-l-propene-3-boronate to give the addition product 271. Reaction of 271 with KH gave the stereochemically pure (Z)-diene 272. Mild acid treatment of 272 followed by... 

This example illustrates that the reactivity of peptide bonds involving serine residues is not due solely to the presence of serine other, as yet poorly understood factors must also play a role. Threonine residues also show this particular type of reactivity [9]. Here, we examine the case of cyclosporin A (CsA), a cyclic undecapeptide that contains some unusual amino acids (6.57, Fig. 6.23), whose major breakdown reaction is hydrolytic cleavage at a threonine analogue. Position 1 is occupied by 4-[( )-but-2-enyl]-A,4-dimethyl-threonine, whose OH group reacts as a nucleophile at the carbonyl C-atom of the adjacent A-methylvalinc (position 11) [86],... 

Unusual amino acids include a class of unnatural a-amino acids such as phenylalanine, tyrosine, alanine, tryptophan, and glycine analogs, and f)-amino acid analogs containing 1,2,3,4-tetrahydroisoquinoline, tetraline, l,2,3,4-tetrahydro-2-carboline, cyclopentane, cyclohexane, cyclohexene, bicyclo[2.2.1]heptane or heptene skeletons. Different selectors were exploited for the separation of unusual amino acids, most of the production being made by Peter and coworkers teicoplanin [41, 56, 84, 90, 93, 124, 141-144], ristocetin A [33, 94, 145, 146], and TAG [56, 147]. Enantiomeric and diastereomeric separations of cyclic -substituted a-amino acids were reported by other authors on a teicoplanin CSP [88, 89], Ester and amide derivatives of tryptophan and phenylalanine were recently analyzed on a Me-TAG CSP [58],... 

Peter, A., Torok, G., and Armstrong, D.W., High-performance liquid chromatographic separation of enantiomers of unusual amino acids on a teicoplanin chiral stationary phase, J. Chromatogr. A, 793, 283, 1998. 

For the purpose of this chapter, all amino acids containing side chains that differ from the L-a-amino acids will be designated as either unusual or nonprotein amino acids. This is due to the observation that these unusual amino acids are generally not found to be the constituents of proteins. The scope of this chapter is limited to nonprotein L-a-amino acids. The definition of nonprotein amino acid is not absolute and, therefore, the... 

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