Fi-hydroxy-a-amino acids

Elimination Reactions from fi-Hydroxy-a-amino Acid Derivatives... 

Glycine-dependent threonine aldolases have been used to synthesize a number of /-halogenated and long-chain fi-hydroxy-a-amino acids. For D-threonine aldolase. vvn-selectivity was observed exclusively. Further chemical conversion yielded the 2-amino-l,3-diols, potential precursors for the synthesis of short-chain sphingo-sine-derivatives (Fig. 35c) [193]. 

Scheme 5.49. Resolution of fi-hydroxy-a-amino acids, using threonine aldolase from Strepto-myces amakusaensis.

Masked chiral a-hetero substituted carboxylic acid enolates have also shown utility in dia-stereoselective additions to nitroalkenes. For example, derivatives of a-hydroxycarboxylic acids, e.g. l,3-dioxolan-4-ones (187) a-amino acids, e.g. 1,3-imidazolidin-4-ones (188) and a-amino-fi-hydroxy-carboxylic acids, e.g. methyl 1,3-oxazolidin-4-carboxylates (189) and methyl l,3-oxazolin-4-carboxy-lates (190), have been employed.1S0a Further, diastereoselective additions of chiral (3-hydroxyesters (191), via the enediolates, to nitroalkenes (40) afford predominant anr/ -P-hydroxyesters (192 Scheme... 

From the ring opening of p-lactams by amines and a-amino acids, p-amino amides and fi-amino acid derived peptides are generated. These structures are of interest because of their presence in several naturally occurring macrocyclic compounds [82, 83]. One example of the latter is the p-hydroxy aspartic acid derived tripeptide 45 found in the macrocyclic peptide lactone antibiotic lysobactin 40 [84], Fig. 4. 

Fltlbener, G., Goehring, W., Musiol, FI. J., and Moroder, L. (1992) N-a-tri-fluoroacetylation of N-terminal hydroxy amino acids a new side reaction in peptide synthesis. Peptide Res. 5, 287-292. 

The 1,3-dipolar cycloaddition of nitrones to alkenes is a useful route to isoxazolidine derivatives, the reductive cleavage of which furnishes a range of compounds such as fi-hydroxy ketones, /S-amino alcohols, etc. [29]. Although Lewis acids are known to promote the cycloaddition [29,30], some nitrones, especially aliphatic nitrones, are unstable under these conditions and lower yields are sometimes obtained. The three-component coupling reaction of benzaldehyde, A/-benzylhydroxylamine, and A-phe-nylmaleimide proceeded smoothly in the presence of a catalytic amount of Sc(OTf)3, to afford the corresponding isoxazolidine derivative in a good yield with high diaster-eoselectivity (Eq. 12) [31]. 

Degradable, synthetic polymers that are commonly known in the medical field include poly(a-hydroxy esters), poly(fi-caprolactone), poly(ortho esters), polyanhydrides, poly(3-hydroxy butyrate), polypho-sphazenes, polydioxanones, polyoxalates, and poly(amino acids). 

Preparation of di-t-buh/lsilylene (DTBS) derivatives The diol, hydroxy acid or amino acid (100 /rg) was dissolved in acetonitrile (30 fA). N-Methylmorpholine (20 1), 1-hydroxybenzotriazole (9 yg) (dried in vacuo at 40 °C prior to preparing the stock solution 3 mg dissolved in 1 ml of acetonitrile and di-t-butylchloro-silane (3.5 fi ) were added sequentially, and the mixture was heated in a Reacti-Vial at 80 °C for 1 h (phenolic substrates and anthranilic acid) or 15 h (other substrates). The resulting solution was diluted to 100/il with ethyl acetate and used for GC and GC-MS analysis. For the derivatization of sterically... 

A class of zinc ion (Zn2+) sensors, which utilized an unnatural amino acid that included the chelation-sensitive fluorophore, 8-hydroxy-4-(Af,Af-dimethylsulfonamido)-2-methylquinoline (sulfonamido oxine (Sox), Figure 1.3a), provided inspiration for a second class of kinase activity sensors [12-14]. The Sox amino acid was prepared via asymmetric synthesis and converted to the fluorenylmethyloxycarbonyl (Fmoc)-protected derivative and incorporated via SPPS into a peptide containing a proline-mediated fi-turn sequence [13]. The fl-turn was flanked by both Zn-chelating amino acids and the Sox fluorophore (Figure 1.3b). In this case, the fi-turn was included to provide preorganization... 

Pseudopoly(amino acids) are polymers derived fi om amino acids with nonamide linkages these are represented by the wavy line in Structures 20,21, and 22. This is usually done by the polymerization of trifunctional amino acids by reaction with side chain functional groups. Three important categories include serine derived polyesters [88] hydroxy-proline derived polyesters, and tyrosine-derived polymers. The first has not been widely used as a biomaterial [89]. The second group consists of poly(A-acyl-hydroxyproline esters) from A-protected hydroxyproline. These polyesters are soluble in benzene, toluene, chloroform, di-chloromethane, carbon tetrachloride, tetrahydrofuran, and dime thy Iformamide. They are thermally stable up to 300 °C, have glass transition temperatures ranging firom 71 °C to 157 °C, and are easily processed [89]. 

Abstract This review is devoted to the stereoselectivity of intermolecular (intramolecular cycloadditions are not included) 1,3-dipolar cycloadditions of sugar-derived nitrones. Stereoselective cycloaddition (transformation of isoxazolidine followed by reduction of the N O bond to produce both an amino and a hydroxy function) allows the synthesis of tailor-made products of possible biological interest such as pol>4iydroxylated pyrrolidines, pyrrolizidines, indolizidines, fi-aminocarbonyl compounds, and disaccharides. Attention is focused on the preparation of isoxazolidinyl nucleosides and to the catalysis of the cycloaddition by Lewis acids. This review has concentrated on the new developments achieved from 1999 to February 2007. 

By a combination of chemical and enzymatic reaction steps, as shown in Scheme 9, cytidine fi-acetylneuraminic acid 5 -phosphate (41) is available from 2-amino-2-deoxy-D-glucose on a multigram scale. Phospholipase D catalyses the regiospecific transfer of alkylphosphoryl residues from alkylphosphorylcholines to primary carbohydrate hydroxy groups. This allowed the efficient, one-step synthesis of D-glucose 6-stearylphosphate and various nucleoside 5 -alkylphosphates from unprotected starting materials. " In the... 

---