Catalytic asymmetric synthesis of protected tryptophan regioisomers

Tryptophan 1 (Trp) is superior to all other naturally occurring peptide residues in its ability to bind cations (the cation-pi interaction). In an effort to expand the toolbox of Trp-like amino acids, in this note we report catalytic asymmetric syntheses of Trp regioisomers 2a-e, where the alanine unit is attached not to C-3 of indole but to C-2, C-4, C-5, C-6, or C-7. Excellent asymmetric induction is obtained in each case (generally >97% ee). Ab initio calculations suggest that the indole nuclei of 2a-e will bind Na(+) with the same affinity as that of Trp.     

Reactivity of dehydroacetic acid in organic synthesis

This review reports the reactivity of dehydroacetic acid, which considered to be a very reactive organic compound. The structure of the title compound was investigated. The condensation reactions with primary amines led to the preparation of a variety of heterocyclic ring systems, including bispyran, pyrazole, thiazole, pyridine, pyrimidine, thiazine, thiazepine, and diazepine ring systems. On the other hand, the condensation reaction with aldehydes led to the formation of 1,5-benzodiazepines, pyran, and pyranopyran heterocyclic ring systems. The reaction mechanisms were discussed. The bibliography includes 130 references.     

Divergent synthesis of D-erythro-sphingosine,L-threo-sphingosine,and their regioisomers

Starting from a vinyl epoxide, a divergent synthesis of four sphingosine isomers is described. The remaining four isomers can easily be synthesized using the same methodology. Although numerous syntheses of sphingosine have been published, this is the first general route leading to all eight isomers in this important compound class. The synthetic strategy relies on regioselective opening of a vinyl epoxide and a vinylaziridine in the allylic position.     

The first synthesis of epoxy-mycolic acids

We report the synthesis of single enantiomers of two epoxy-mycolic acids containing an α-methyl-trans-alkene.     

The synthesis of amides of halonitrocarboxylic acids

Amides of 2-nitro-3,3,3-trifluoro-2-chloropropionic, 2-nitro-3,3-difluoro-2,3-dichloropropionic, and nitrodichloroacetic acids were obtained by the ammonolysis of the acid chlorides of the corresponding halonitrocarboxylic acids.Translated from Izvestiya Akademii Nauk SSSR. Seriya Khimicheskaya, No. 4, pp. 927–928, April, 1990.     

The synthesis of brassylic and 1,12-dodecanedicarboxylic acids

Summary A method has been worked out for the synthesis of brassylic and 1, 12-dodecanedicarboxylic acids, starting from cyclododecanone and cyclotridecanone.     

The synthesis of tetrafluoro-sulphobenzoic acids and their derivatives

The tetrafluorosulphobenzoic acids 1,2-HO₂C.C₆F₄.SO₃H (I) and 1,4-HO₂C.C₆F₄.SO₃H (II) have been synthesised [1] by oxidation of respectively 4,5,6,7-tetrafluorobenzo [b] thiophen- 2-carboxylic acid (III) [2] and 4-mercaptotetrafluorobenzoic acid (IV) [3].By-products were obtained when (III) was oxidised with either trifluoroperacetic acid or potassium permanganate.A number of reactions of these intermediates have been investigated and the products characterized, eg reaction of (I) with SoCl₂ gave tetrafluoro-1,2-sulphobenzoic acid cyclic anhyride (V). Although no significant change was observed when (II) was similarly treated reaction of (II) with DMF/SOCl₂ gave 1,4-Cl.C₆F₄.COCl. The diacid fluorides 1,2-FOC.C₆F₄.SO₂F (VI) and 1,4-FOC.C₆F₄.SO₂F (VII) were obtained when (I) and (II) respectively were reacted with sulphur tetrafluoride. The use of excess SF₄ gave 1,2- or 1,4- [F₃C.C₆F₄.SO₂F].     

Capillary electrophoresis analysis of glucooligosaccharide regioisomers

Complex gluco-oligosaccharide mixtures of two regioisomer series were successfully separated by CE. The gluco-oligosaccharide series were synthesized, employing a dextransucrase from Leuconostoc mesenteroides NRRL B-512F, by successive glucopyranosyl transfers from sucrose to the acceptor glucose or maltose. The glucosyl transfer to both acceptors, occurring through the formation of alpha1-->6 linkages, differed for the two series only in the glucosidic bond to the reducing end namely alpha1-->6 or alpha1-->4 bond for glucose or maltose acceptor, respectively. Thus, the combination of the two series results in mixed pairs of gluco-oligosaccharide regioisomers with different degrees of polymerization (DP). These regioisomer series were first derivatized by reductive amination with 9-aminopyrene-1,4,6-trisulfonate (APTS). Under acidic conditions using triethyl ammonium acetate as electrolyte, the APTS-gluco-oligosaccharides of each series were separated enabling unambiguous size determination by coupling CE to electrospray-mass spectrometry. However, neither these acidic conditions nor alkaline buffer systems could be adapted for the separation of the gluco-oligosaccharide regioisomers arising from the two combined series. By contrast, increased resolution was observed in an alkaline borate buffer, using differential complexation of the regioisomers with the borate anions. Such conditions were also successfully applied to the separation of glucodisaccharide regioisomers composed of alpha1-->2, alpha1-->3, alpha1-->4, and alpha1-->6 linkages commonly synthesized by glucansucrase enzymes.     

Separation of regioisomers and enantiomers of triacylglycerols containing branched fatty acids (iso and/or anteiso)

A combination of two chromatographic and one enzymatic methods was used for identification of the molecular species of triacylglycerols (TAGs) from Streptomyces avermitilis. Streptomyces avermitliswas cultured on various carbon sources and the ratio of iso- (i-FAs), anteiso- (ai-FAs), and straight-chain- (n-FAs) fatty acids was modified by precursor-directed biosynthesis. Saturated TAGs were separated from other lipids (including TAGs containing unsaturated FAs) using Ag⁺ ion cartridges. Analysis of TAGs wereperformed by RP-HPLC/ESI⁺ tandem mass spectrometry. Both the synthetically prepared sn-TAGs and the natural mixture of TAGmolecular species of wereseparated and identified by tandem MS. The structures of synthetic TAGs werefurther confirmed by pancreatic lipase, which cleaves sn-TAGs into sn-2-monoacylglycerols. The retention times (tR) of the individual regioisomers and enantiomers were found to be depend on the structure of the TAGs. If one branched acyl (iso or anteiso) is present in the TAG molecule, then the elution order is enantiomer (n/n/br), opposite enantiomer (br/n/n), regioisomer (n/br/n). In the case where two branched acyls are in the TAG molecule, the order of the elution is different, that is, br/n/br, n/br/br, br/br/n. In all cases, it was further demonstrated that tandem MS of either synthetically prepared TAGs or TAGs obtained from natural material, that is, n-16:0/ai-15:0/n-16:0 and i-16:0/n-15:0/i-16:0 are identical. Unfortunately, it is not possible to distinguish by ESI⁺ tandem MS such TAGs, which differ only in the branching of the acyls. The results of our analyses of TAGs are in good agreement with previously published data in other streptomycetes.     

The first synthesis of single enantiomers of ketomycolic acids

We report the synthesis of single enantiomers of two protected ketomycolic acids, one containing a cis-cyclopropane the other an α-methyl-trans-cyclopropane, and of related hydroxy-mycolic acids.     

The synthesis of bisitaconamic acids and isomeric bisimide monomers

Members of a series of N,N′-alkylene bisitaconamic acids were synthesized from the reaction between itaconic anhydride and a homologous group of aliphatic diamines with the general formula H₂N (CH₂)_n NH₂, where n = 4–12. Cyclodehydration of the acids in toluene gave the isomeric imides: bisitaconimide, biscitraconimide, and citra-itaconimide. The isomeric imides were isolated, purified, and characterized for each diaminoalkane studied.     

The first aminoacylase-catalyzed enantioselective synthesis of aromatic beta-amino acids

The first aminoacylase-catalyzed enantioselective synthesis of aromatic beta-amino acids is reported. The presence of an N-chloroacetyl group as acyl group in the substrate as well as the use of porcine kidney acylase I as a suitable enzyme component are prerequisites for this resolution process whereby optically active beta-amino acids are formed with high enantioselectivities of >98% ee.