Preparation of the Chiral Diol (2R,3R)-2-Hydroxymethyl-3-hydroxy-tetrahydropyran from D-Glucose via Reductive Rearrangement of Pseudo-D-glucal Triacetate

Hydrogenation of n-glutal triacetate (1) and pseudo-n-glucal triacetate (2) into (2R,3R)-2-acetoxymethyl-3-acetoxy-tetrahydropyran (4) and the rearrangement of 1 into 2 were investigated. On. hydrogenation, at high catalyst-to-substrate ratio and in the presence of a great excess of diethylamine, compound 1 afforded diacetate 4 in a mixture with triacetate 6, while 2 was quantitatively converted into 4 under standard catalyst-to-substrate (- 1 : 80) ratio. It was established that hydrogenation of both isomers proceeds through the same intermediate 4,6-di-O-acetyl-l,2,3-trideoxy- n-erythro-hex-J-enitol (3) which was fully characterised from its lH_ and 13C-NMRspectra. When hydrogenation of 2 was performed with platinum on carbon in acetonitrile, compound 3 was isolated in 83010yield. The thermal and Lewis acid catalysed rearrangement of 1 into 2 was examined; only zinc(II) chloride in acetic anhydride gave preparatively acceptable yields (60- -70010) of 2. It was demonstrated that with Zn(II) or Mo(VI) ions in AC20 an 1 =:; 2 equilibrium in favour of 2 was attained

Preparation of the Chiral Diol (2R,3R)-2-Hydroxymethyl-3-hydroxy-tetrahydropyran from D-Glucose via Reductive Rearrangement of Pseudo-D-glucal Triacetate

Hydrogenation of n-glutal triacetate (1) and pseudo-n-glucal triacetate (2) into (2R,3R)-2-acetoxymethyl-3-acetoxy-tetrahydropyran (4) and the rearrangement of 1 into 2 were investigated. On. hydrogenation, at high catalyst-to-substrate ratio and in the presence of a great excess of diethylamine, compound 1 afforded diacetate 4 in a mixture with triacetate 6, while 2 was quantitatively converted into 4 under standard catalyst-to-substrate (- 1 : 80) ratio. It was established that hydrogenation of both isomers proceeds through the same intermediate 4,6-di-O-acetyl-l,2,3-trideoxy- n-erythro-hex-J-enitol (3) which was fully characterised from its lH_ and 13C-NMRspectra. When hydrogenation of 2 was performed with platinum on carbon in acetonitrile, compound 3 was isolated in 83010yield. The thermal and Lewis acid catalysed rearrangement of 1 into 2 was examined; only zinc(II) chloride in acetic anhydride gave preparatively acceptable yields (60- -70010) of 2. It was demonstrated that with Zn(II) or Mo(VI) ions in AC20 an 1 =:; 2 equilibrium in favour of 2 was attained

Preparation of Chiral Diphenylphosphines from D-Glucose and Enantioselective Hydrogenation with Their Rh(l) Complexes

(2R,3S)-2-Methylsulfonyloxymeihyl-3-methylsulfonyloxy-tetrahydropyran (4), derived from n-glucose, is diphenylphosphinated to (2R,3R)-2-diphenylphosphinomethyl-3-diphenylphosphino-tetrahydropyran (7), which is formed as aminor product. Compound 8 is the predominant product, formed on 3,4-elimination. Preparation and characterization of the rhodium(I) complexes 10-12 is described. Complex 10 of bidentate Iigand 7 exhibits in hydrogenation of Z-a-N-acetylaminocinnamic acid enantioselectivity comparable to that obtained with rhodium(I) complex of (-)-DIOP (-70010e. e.). Saturated monophosphine, (2S)-2-diphenylphosphinomethyl-tetrahydropyran (9) affords mixed rhodium(I) complex (11, 12), which exhibits low enantioselectivity

Study on the Lewis Acid-promoted Aza-Diels - Alder Reaction of Azetidin-2-one-tethered Imines with Siloxydienes in the Asymmetric Synthesis of 2-Aryl(alkyl)-2,3-dihydro-4-pyridones

trans-3-Amino-b-lactams were evaluated as the chiral building blocks in the aza-Diels – Alder reaction of azetidin-2-one-tethered imines with siloxydienes under Lewis acid catalysis, as a route for the asymmetric synthesis of 2-aryl(alkyl)-2,3-dihydro-4-pyridones

Ferrocene Compounds. XII*. Reactions of Ferrocenecarbaldehyde with Benzanilides and n-Butyllithium

The reactions of ferrocenecarbaldehyde with benzanilides, and n-butyllithium, depending on the benzanilide used, gave mixtures of 1-hydroxypentylferrocene, 1-phenoxypentylferrocene, pentylferrocene, hydroxymethylferrocene, bis(ferrocenylmetyl) ether and ferrocene. The mixtures obtained have been separated into pure components by chromatographic methods and their structures have been assigned by spectroscopic means

Preparation and Properties of Some Pro chiral and Chiral Precursors of S-3-(3-Hydroxyphenyl)-1-propylpiperidine (S-3-PPP)

Various synthetic approaches to 2,3-dehydro- and 3,4-dehydro-1-propio- nylpiperidines 12,13 and to their 1-propyl congeners 14,15,-two pairs of unsaturated, regioisomeric precursor of S-(-)-3-PPP [S-(-)-3-(3-hydroxyphe- nyl)-l-propylpyperidine, 20] were investigated. Compounds 12 and 13 were prepared by regioselective elimination of water in 11. Preparation of 14 and 15 by two different methods is described. The ratio of the E/Z isomers at the C(0)-N bond in 11-13 was determined by 13C-NMR, and separation of the enantiotopic XH-NMR signals in the enantiomers of 18 and 19 was investigated with chiral shift reagent Eu(tfc>3. Hydrogenation of 15 was performed with five different Rh(l) catalytic complexes, affording the O-methyl-conge- ner of 3-PPP 19. Complete conversion of 15 into 19 was only achieved at elevated temperature and/or pressure to give the R- or S-isomer with low enantioselectivity (7-18% e.e.)

Influence of peptide and amino acids on the formation of cheese flavour

U sirevima se tijekom zrenja odvijaju kompleksne mikrobiološke i biokemijske promjene koje imaju značajan utjecaj na formiranje organoleptičkih karakteristika gotovog proizvoda. Proteolitički enzimi razgrađuju kazein do većih i manjih peptida te slobodnih aminokiselina. Količina i omjeri pojedinih aminokiselina i topljivih peptida znatno utječu na teksturu i organoleptička svojstva sira. Razgradnjom aminokiselina u siru nastaju alkoholi, aldehidi, esteri, kiseline i sumporni spojevi koji formiraju specifične arome raznih vrsta sireva. U siru je identificirano više od 200 različitih hlapljivih komponenti. Okus sira je koncentriran u frakciji topljivoj u vodi (peptidi, aminokiseline, organske kiseline i amini), dok je aroma uglavnom koncentrirana u hlapljivoj frakciji (organske kiseline, aldehidi, amini, esteri). Mnogi sirevi sadrže iste ili slične komponente, ali u različitim koncentracijama i odnosima. Posebnosti arome sira ne zasnivaju se samo na jednom specifičnom spoju već na kombinaciji različitih spojeva nastalih tijekom zrenja. Djelovanjem na proteolitičke procese može se ubrzati i modificirati tehnološki proces proizvodnje sira, te ih se stoga intenzivno proučava.Complex microbiological and biochemical changes take place during cheese ripening process, having a significant impact on the formation of organoleptic characteristics of the final product. Proteolytic enzymes degraded casein to larger and smaller peptides and free amino acids. The quantity and the ratios of particular amino acids and soluble peptides significantly influence the texture and organoleptic properties of cheese. The products of amino acid degradation in cheese are alcohols, aldehydes, esters, acids and sulphur compounds, which form specific aromas of various cheese types. More than 200 different volatile components have been identified in cheese. Cheese flavour is concentrated in the watersoluble fraction (peptides, amino acids, organic acids and amines), while aroma is mainly concentrated in the volatile fraction (organic acids, aldehydes, amines, esters). Many cheeses contain the same or similar components, but in different concentrations and ratios. Specific characteristics of cheese aroma are not based only on one specific compound, but on combination of different compounds produced in the maturing process. The technological process of cheese production can be accelerated and modified by influencing proteolytic processes, which are therefore the subject of intense research

Novel amino-β-lactam derivatives as potent cholesterol absorption inhibitors

Two new trans-(3R, 4R)-amino-β-lactam derivatives and their diastereoisomeric mixtures were synthesized as ezetimibe bioisosteres and tested in in vitro and in vivo experiments as novel β-lactam cholesterol absorption inhibitors. Both compounds exhibited low cytotoxicity in MDCKII, hNPC1L1/MDCKII, and HepG2 cell lines and potent inhibitory effect in hNPC1L1/MDCKII cells. In addition, these compounds markedly reduced cholesterol absorption in mice, resulting in reduced cholesterol concentrations in plasma, liver, and intestine. We determined the crystal structure of one amino-β-lactam derivative to establish unambiguously both the absolute and relative configuration at the new stereogenic centre C17, which was assigned to be S. The pKa values for both compounds are 9.35, implying that the amino-β-lactam derivatives and their diastereoisomeric mixtures are in form of ammonium salt in blood and the intestine. The IC50 value for the diastereoisomeric mixture is 60 μM. In vivo, it efficiently inhibited cholesterol absorption comparable to ezetimibe