Synthesis and proposed conformations of l-prolyl-l-leucyl-β-alanine alkylamides

The synthesis of H-Pro-Leu-β-Ala-NH₂, H-Pro-Leu-β-Ala-NHCH₃ and H-Pro-Leu-β-Ala-N(CH₃)₂ is described. On the basis of IR and ¹H NMR spectral data, a 7-membered ring including the NH of β-alanine with the CO of proline should be assigned for the H-Pro-Leu-β-Ala-N(CH₃)₂. Consequently, the plausible conformations for H-Pro-Leu-β-Ala-NH₂ and H-Pro-Leu-β-Ala-NHCH₃ derive from the formation of an 11-membered ring, between the trans amide proton and the CO of Pro, or from the formation of an 8-membered ring, between this carboxamide proton and the CO of Leu, plus the aforementioned 7-membered ring.     

Synthèse d'analogues de dérivés dioxaprostanoïques à partir du d et du l-xylose

Epoxides 7, 8 and 9 have been prepared from d and l-xylose, and used for the synthesis of a precursor of ent-(11-oxa)PG 19 and of 9,13-and 7,11-dioxaprostanoïc acids 28 and 31. The site of the opening of the epoxidcs 7 and 9 with the carbanion derived from bis-(phenylth)romethane and with LiAlH₄ is shown by establishing structures of the products 11, 12, 20 et 21 by ¹³CNMR spectroscopy.     

Stereoselective synthesis of l-isonucleosides

l-Isonucleosides 17 and 19 were stereoselectively synthesised from (S)-glycidol by two different procedures. The key step was the synthesis of a chiral dihydrofuran which was carried out by oxidation/elimination of 8 and by ring-closing metathesis of diene 10. The procedure can be applied to the synthesis of both enantiomers.     

Concise and divergent approach to 3-O-acyl-l-noviose derivatives and their 3-amino bioisosteres: 3-O-benzoyl-l-noviose and N-benzoyl-3-amino-l-noviose

Generally applicable concise approaches to 3-O-acyl-l-noviose derivatives and their 3-amino bioisosteres, represented by 5 and 6, were described. Chiral aldehyde 7 was thus prepared from dimethyl l-tartrate in five steps, and converted into 5 and 6 by employing substrate induced asymmetric aldehyde or N-sulfinyl aldimine allylation and dihydropyrane epoxidation as key steps, respectively.     

Some new ring-D seco steroids

The Beckmann fragmentation product, 3-methoxy-17-oxo-16,17-secoestra-1,3,5(10)-trien-16-nitrile (2) has been reduced by LAH giving the expected 3-methoxy-17-hydroxy-16,17-secoestra-1,3,5(10-trien-16-amine hydrochloride (3) and 3-methoxy-17-oxa-D-homoestra-1,3,5(10)-trien-16-ol (4), by a presumed neighbouring group participation of 17-OH group in the intermediary formed 16-imino derivative (A). The structure of 4 has been proved by an alternative synthetic route by reducing 3-methoxy-17-oxa-D-homoestra-1,3,5(10)-trien-16-one (7) with di-iso-butylaluminium hydride.     

Synthesis of 1-deoxy-l-gulonojirimycin and 1-deoxy-l-talonojirimycin

De novo synthesis of noncompetitive glycosidase inhibitors l-gulo-DNJ and l-talo-DNJ has been achieved in 9-10 steps starting from Garner’s aldehyde. Key to the success of this procedure was the construction of the 2,3-unsaturated piperidine 14, which syn dihydroxylation under Kishi’s and Donohoe’s conditions led to the desired iminosugars.     

Regio- and stereoselective syntheses of l-pentose derivatives from l-arabinose

Novel l-arabinose, l-ribose, 2-deoxy-l-ribose and 2-fluoro-2-deoxy-l-arabinose derivatives were synthesized from readily available l-arabinose. Different synthetic routes to methyl 3,5-di-O-acylated-l-arabino(ribo)furanosides as valued intermediates for the preparation of C-2 functionalized l-pentoses were investigated via regioselective transformations of 1,2-di-O-acetyl-3,5-di-O-pivaloyl-l-arabinofuranose, and selective acylation of methyl l-arabinofuranoside with 4-chlorobenzoyl or pivaloyl chloride. Short three-five-step syntheses of methyl 2-deoxy-α-l-ribofuranoside, its 3,5-di-O-acyl derivatives, valuable precursors for preparation of antiviral 2′-deoxy-l-nucleosides, were accomplished via simple and efficient reduction of methyl 2-O-mesyl-l-arabinofuranoside with L-Selectride or tandem reaction involving a complex hydride 2-deoxygenation/acylation of intermediate 2-deoxysugar. A new synthesis of 2′-deoxy-2′-fluoro-β-l-arabinofuranosyl thymine (l-FMAU) was performed using a mild fluorination of protected l-ribofuranoside and a novel sequence of conversions for the preparation of 2-deoxy-2-fluoro-l-arabinofuranoside derivatives.     

Synthese de cetoses a chaine ramifiee dans la serie du d-fructose et du d-psicose

Stereospecific synthesis of branched-chain 3-C-formyl, 3-C-hydroxymethyl and 3-C-methyl derivatives of d-psicose have been achieved via nucleophilic C-acylation by means of the 1,3-dithian carbanion of 1,2:4,5-di-O-isopropylidene-β-d-erythro-hexo-2,3-diulo-2,6-pyranose 1. Addition of nitromethane to 1 led to d-psicose and d-fructose derivatives 8 and 9.     

Synthesis of d-gluco-, l-ido-, d-galacto-, and l-altro-configured glycaro-1,5-lactams from tartaric acid

The d-gluco-, l-ido-, d-galacto-, and l-altro-configured glycaro-1,5-lactams 1-4 were prepared from the known tartaric anhydride 5 via the aldehyde 6. These lactams are known (1) or potential (2-4) inhibitors of β-d-glucuronidases and α-l-iduronidases. Olefination of 6 to the (E)- and (Z)-alkenes 7 or 8, followed by reagent or substrate controlled dihydroxylation, lactonization, azidation, reduction, and deprotection led in 10 steps and in overall yields of 11-20% to the title lactams.     

Total synthesis of 3-deoxy and 3,6-dideoxy-dl-hexoses

Synthesis of stereoisomeric 3-deoxy-hexoses 24–27 and 3,6-dideoxy-hexoses 28–31 is reported. Butyl (E)-2,6-dihydroxy-hex-4-enoate (2) was used as the starting material for the synthesis of 3-deoxy-hexoses. For the synthesis of 3,6-dideoxy-hexoses, butyl (E)-2-acetoxy-hex-4-enoate (7) was employed. The synthesis involved the following successive steps: cis or trans hydroxylation of the double bond in 2 or 7, lactonisation of the resulting aldonic acid esters followed by acetylation and chromatographical separation of γ-lactones, reduction of lactones 16–23 to lactols with disiamylborane, and acetylation of lactols to free sugars. All compounds were obtained as pure diastereomers in racemic form.     

One-pot synthesis of N-Cbz-l-BMAA and derivatives from N-Cbz-l-serine

We report herein an asymmetric synthesis of the modified amino acid N-Cbz-l-BMAA and seven of its alkyl derivatives (2a-h) from N-Cbz-l-serine via ring-opening of the β-lactone (formed under modified Mitsunobu conditions) by different amines. This procedure is simple, one-pot and can generate various derivatives that can be investigated for their toxicological effects. In addition, it can be employed to produce analytical standards for water monitoring as well as labeled compounds for biotransformation studies. This toxin has been the focus of serious ecological and public concern since its implication in degenerative disease such as Alzheimer and Parkinsonism dementia.     

An efficient synthesis of 1,4-dideoxy-1,4-imino-d- and l-arabinitol and 1,4-dideoxy-1,4-imino-d- and l-xylitol from chiral aziridines

A highly efficient method for the synthesis of 1,4-dideoxy-1,4-imino-d- and l-arabinitol (d-AB1, 1 and l-AB1, 3) and 1,4-dideoxy-1,4-imino-d- and l-xylitol (d-DIX, 2 and l-DIX, 4) starting from commercially available chiral aziridines was developed. The general strategy employs a sequence involving two-carbon homologation, dihydroxylation, and regioselective aziridine ring opening/intramolecular five-membered iminosugar ring formation. The facile use of recrystallization to generate pure diastereomers makes the routes more amenable to large-scale synthesis.     

Glycine and l-glutamic acid-based dendritic gelators

Novel dendrons based on glycine and l-glutamic acid from the first generation (G1) to the third generation (G3) were synthesized and studied for their gelation properties by using transmission electron microscopy (TEM), atomic force microscopy (AFM), fluorescence, IR, circular dichroism (CD), and ¹H NMR spectroscopy. It was found that the gelation capability of these dendrons increased from the first generation (G1) to the third generation (G3), and that G3 exhibited the highest efficiency in forming gels. Both the focal and peripheral groups of dendrons had great effects on the formation of organogels. Hydrogen bonding and π-π stacking interactions were proved to be the main driving forces to form the fibrous networks at low concentrations (0.5 wt %). Small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) measurements indicate that the xerogels of the second generation (G2) from ethyl acetate and ethanol, and G3 xerogel from CH₂Cl₂ all display lamellar structures with the interlamellar spacing of ca. 36.0 Å for G2 and 40.5 Å for G3, respectively.     

Enzymatic determination of l-lysine by flow-injection techniques

An enzymatic assay that is highly selective for l-lysine, based on flow-injection techniques combined with spectrophotometric detection, is presented. l-Lysine-α-oxidase (E.C. 1.4.3.14) from Trichoderma viride and horseradish peroxidase were used in a coupled enzyme assay. Peroxide produced in the first reaction was converted by peroxidase with phenol and 4-aminoantipyrine to a quinoneimine dye detectable at 500 nm. An analytical enzyme reactor filled with coimmobilized enzymes was incorporated in the flow-injection system. The assay has a measuring frequency of 30 samples h^?1 and a response time of less than 2 min. To adapt the assay to high concentrations of l-Lysine and to minimize interferences, the injected sample volume was reduced to 2 μ-l, resulting in a linearity range of 1–16 mM l-lysine with a sensitivity of 6–7 mV 1 mmol^?1, a limit of detection (3σ) of 1 mM and a reproducibility of 0.5% (repetitive injection of a 10 mM l-lysine sample). The enzyme cartridge is stable for several months and thousands of measurements.     

Synthesis of tadalafil (Cialis) from l-tryptophan

The first synthesis of tadalafil 1 (Cialis) from l-tryptophan is described. The title compound 1 was synthesized via seven steps from l-tryptophan methyl ester hydrochloride in 42.3% overall yield. Two characteristic steps involved in this synthesis are the base-catalyzed epimerization of the C-3 position of (1S,3S)-1,2,3-trisubstituted-tetrahydro-β-carboline 3a and the acid-catalyzed epimerization of the C-1 position of (1S,3R)-1,3-disubstituted-tetrahydro-β-carboline 5. The (S)-configurations at C-1 and C-3 were inverted to (R)-configurations during the epimerization reactions. The base-catalyzed epimerization of C-3 of (1S,3S)-1,2,3-trisubstituted-tetrahydro-β-carbolines 3a–3e was also studied in detail.     

d-Phg-l-Pro Dipeptide-derived prolinol ligands for highly enantioselective Reformatsky reactions

Optically pure N-aminoethyl prolinol derivatives 3a-c have been prepared from the dynamic kinetic resolution of N-(α-bromo-α-phenylacetyl) proline ester 1 in asymmetric nucleophilic substitution and subsequent reduction. The peptide-derived prolinols are tested as chiral ligands in the asymmetric addition of Reformatsky reagent to aromatic aldehydes. Chiral ligand 3c has been shown to be effective to produce enantioenriched β-hydroxy esters 5a-j with up to 98% ee.     

An efficient synthesis of d-ribo- and l-lyxo-phytosphingosine from d-tartaric acid

The preparations of d-ribo- and l-lyxo-phytosphingosines (1, 2) are described. Chelation-controlled addition of tetradecylmagnesium bromide to pentylidene-protected d-threitol aldehyde 6 afforded the key intermediate tetrol 7, providing the desired l-lyxo stereochemistry of phytosphingosine. Inversion at C4 of intermediate 7 provided the d-ribo stereochemistry.     

The first chemical conversion of l-proline to l-glutamic acid

The ruthenium tetroxide oxidation of N-acyl-l-proline esters gave the corresponding l-pyroglutamic acid derivatives in good yields with no appreciable racemization, which led to the first chemical conversion of l-proline to l-glutamic acid.     

A new synthesis of four diastereoisomeric 2,6-dideoxy-dl-hexoses

The synthesis of four diastereoisomeric 2,6-dideoxy-DL-hexoses from butyl E 2,3,4-trideoxy-aldehydo-DL-hex-2-enuronate (2) is described. The aldehyde 2 treated with MeMgBr affords a mixture of diastereoisomeric diols 6, which after hydroxylation and Ruff degradation gives 2,6-dideoxy-DL-hexoses 13,14, 15 and 16.     

Resonant cars spectroscopy of s-tetrazine vapour

CARS experiments on s-tetrazine vapour show that the electronic resonance enhancement in the Q-branch is most effective for the lower J values. This suggests that the radiationless relaxation rate in the excited state increases with rotational quantum number. Delayed picosecond CARS experiments indicate that the rotation-vibration coupling for the 1008 cm^?1 ground-state vibrational mode is approximately 2 MHz.