47004-38-6

The tert-butoxycarbonyl protecting group for amines, alcohols, and thiols was removed efficiently (90-99% yields) by use of 0.20 equivalent of Ce(NH4)2(NO3)6 in acetonitrile.

Enantiomers of a series of tripeptide derivatives with three stereogenic centers (±)-G1-G9 have been prepared from d- and l-α-amino acids as guests for chiral recognition by 1H NMR spectroscopy. In the meantime, a family of tetraaza macrocyclic chiral solvating agents (TAMCSAs) 1a-1d has been synthesized from d-phenylalanine and (1S,2S)-(+)-1,2-diaminocyclohexane. Discrimination of enantiomers of (±)-G1-G9 was carried out in the presence of TAMCSAs 1a-1d by 1H NMR spectroscopy. The results indicate that enantiomers of (±)-G1-G9 can be effectively discriminated in the presence of TAMCSAs 1a-1d by 1H NMR signals of multiple protons exhibiting nonequivalent chemical shifts (ΔΔδ) up to 0.616 ppm. Furthermore, enantiomers of (±)-G1-G9 were easily assigned by comparing 1H NMR signals of the split corresponding protons with those attributed to a single enantiomer. Different optical purities (ee up to 90%) of G1 were clearly observed and calculated in the presence of TAMCSAs 1a-1d, respectively. Intermolecular hydrogen bonding interactions were demonstrated through theoretical calculations of enantiomers of (±)-G1 with TAMCSA 1a by means of the hybrid functional theory with the standard basis sets of 3-21G of the Gaussian 03 program.

Over 50 years ago, Jencks and Gilchrist showed that formaldehyde catalyses the hydrolysis of phosphoramidate through electrophilic activation, induced by covalent attachment to its nitrogen atom. Given our interest in the use of aldehydes as catalysts, this work was revisited to identify a superior catalyst, o-phthalaldehyde, which facilitates hydrolyses of various organophosphorus compounds bearing P(O)-NH subunits under mild conditions. Interestingly, chemoselective hydrolysis of the P(O)-N bonds could be accomplished in the presence of P(O)-OR bonds.

The first strategy for bringing about enantioselective azlactone dynamic kinetic resolution to generate orthogonally protected amino acids has been developed. In the presence of a C2-symmetric squaramide-based catalyst, benzyl alcohol reacts with novel yet readily prepared tetrachloroisopropoxycarbonyl-substituted azlactones to generate trapped phthalimide products of significant synthetic interest with excellent enantiocontrol. These materials are masked amino acids which are demonstrably orthogonally protected: cleavage of the phthalimide can be achieved in the presence of the ester and vice versa. This process could be utilized to bring about a highly stereoselective ligation-type coupling of protected serines (at stoichiometric loadings) with racemic azlactones derived from both natural and abiotic amino acids. After deprotection, a subsequent base-mediated Oa??N acyl transfer occurs to form a dipeptide.

The monoanions of nitroalkanes are ambident nucleophiles that react with carbonate electrophiles through the oxygen atom. Products arising from reactivity at the carbon atom will yield α-nitro esters, which are precursors for α-amino esters. We demonstrate this in the reactions of nitroalkanes with benzyl phenyl carbonate and DABCO where α-nitro esters are obtained instead of nitrile oxides. The products are readily reduced to α-amino esters. This pathway could be a safe alternative to the Strecker reaction.

In this study, the competing benzyl cation transfer reactions have been explored by investigating the gas phase chemistry of the protonated benzyl phenylalaninates. Protonation at the carboxylic O atom results in the breakage of the ester CO bond to afford the benzyl cation, which undergoes the competing migration to the amino N atom or the phenyl ring C atom. Both the amino and the phenyl ring hydrogen atoms can be activated to be mobile due to the electrophilic attack of the transferring benzyl cation, and migration of the activated hydrogen atom to the carboxylic hydroxyl leads to (H2O + CO) elimination of the precursor ion. Interestingly, it is much more preferred for the benzyl cation to transfer to the phenyl ring via the amino N, leading to the stepwise benzyl cation transfer, albeit the amino N atom contains more nucleophilic affinity. The mechanistic processes have been confirmed by the MS3 spectra data, along with D-labeling experiments and theoretical calculations.

Enantioselective cyclization of α-isocyano esters with azodicarboxylates catalyzed by FeII-N,N′-dioxide complexes has been developed. Under mild conditions, a variety of 1,2,4-triazoline derivatives was obtained in high yields and enantioselectivities.

A concise protocol for the synthesis of α-methylene-β-hydroxy- γ-carboxy-γ-lactams has been described via alkylation of amino acid derived iminoesters with α-bromomethylmethacrylate, followed by allylic hydroxylation. All the synthesized compounds have been evaluated for their cytotoxicity on multiple myeloma cancer cell lines.

A novel methodology for the efficient synthesis of [2.2.1] heterobicyclic pyroglutamates has been described. The key synthetic steps involve alkylation of amino acid-derived iminoesters with Baylis-Hillman bromide, RhCl 3-catalyzed exocyclic olefin isomerization, diastereoselective dihydroxylation, and regioselective lactonization. All the compounds were evaluated for their cytotoxicity using multiple myeloma cancer cell lines RPMI 8226.

The present invention describes compounds produced from an orotic acid molecule and an amino acid molecule. The compounds being in the form of amino acid orotate compounds bound by an amide linkage and produced by one of two disclosed methods; 1) reacting orotic acid or derivatives thereof with a thionyl halide, and then combining the acyl halide with an amino acid in the presence of dichloromethane and a DMAP catalyst; or 2) protecting the carboxylic acid of an amino acid and then combining the amino acid with a DCC activated orotic acid, followed by removal of the carboxylic acid protecting group. The resulting amino acid orotate amide has an enhanced stability in solution as compared to a related ester. In addition, specific benefits are conferred by the particular amino acid used to form the compounds in addition to, and separate from, the orotate substituent.

A convenient procedure for the racemization of α-amino acid esters in the presence of catalytic amounts of salicylaldehydes is described. The combination of this racemization protocol with lipase-catalyzed ester hydrolysis allows successful dynamic kinetic resolution of various α-amino acid esters. The corresponding α-amino acids are obtained in high yield and optical purity. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

The capillary zone electrophoresis using (+)-18-crown-6-tetracarbonic acid as a chiral selector was a suitable method for the enantiomeric separation of racemates of amino acids and of some amino acid derivatives (esters, dipeptides). The influence of the chemical structure of the compounds on the separation was investigated. After optimization of the separation conditions, baseline separations were obtained for most racemates. The addition of acetonitrile and TBAB yielded an improvement of the separation. Improved selectivity was further observed by the application of a cyclodextrin, HP-β-CD, in combination with the crown ether.

The synthesis of 10 new T-PNA monomers derived from L-amino acids is presented. The monomers were incorporated into decameric PNA oligomers, and the hybridisation with RNA, DNA and PNA complements studied by thermal stability measurements.

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Selective activation of 3-hydroxy-2-hydroxymethyl-2-methylpropanamide with P(NMe2)3-CCl4, and subsequent intramolecular cyclisation yields β-lactam derivatives that have both surface and antibiotic activity.

The diketopiperazine cyclo(-L-Val-Gly-) (1) can be O-alkylated under mild acidic reaction conditions with the alkyl trichloroacetimidates 2 to the corresponding bisalkyl bislactim ethers.Alkylation of the bisbenzyl bislactim ether anion of cyclo(-L-Val-Gl