Stereoselective synthesis of cis-p-menth-8-ene-1,7-diol, cis-p-menthane-1,7-diol, and cis-p-menthane-1,7,8-triol

The natural products cis-p-menthane-1,7-diol (cis-IV), cis-p-menth-8-ene-1,7-diol (cis-I) and cis-p-menthane-1,7,8-triol (cis-II) are obtained starting from the corresponding cis-cyanohydrins, cis-2 and cis-7, respectively, by chemical transformation of the cyano into the hydroxymethyl group. The key step of the synthesis is the very high cis-selectivity (> or = 96 %) of the MeHNL-catalyzed HCN addition to 4-alkylcyclohexanones. From 4-isopropylcyclohexanone (1) the cyanohydrin cis-2 and from 4-(1-methylvinyl)cyclohexanone (6) the cyanohydrin cis-7 result almost quantitatively. Regioselective hydroxylation of cis-I affords the triol cis-II. X-ray crystal structure determinations of the final products confirm their cis-configuration.     

PHOTOREGULATION OF α-CHYMOTRYPSIN ACTIVITY IN ORGANIC MEDIA: EFFECTS OF BIOIMPRINTING

Abstract α-Chymotrypsin exhibits photoswitchable activities in an organic solvent after covalent modification of the protein backbone with thiophenefulgide active ester (2). The thiophenefulgide-modified α-chymotrypsin exhibits reversible photoisomerizable properties between states (3)-E and (3)-C. The modified α-chymotrypsin, where nine lysine residues are substituted by thiophenefulgide units, retains 60% of the activity of the native enzyme. The activities of thiophenefulgide-modified α-chymotrypsin toward esterification of N -acetyl-L-phenylalanine (4) by ethanol in cyclohexane are controlled by the configuration of the attached photoisomerizable component and by prior bioimprinting of the protein backbone with the reaction substrate (4). The esterification of (4) in cyclohexane using bioimprinted (3)-C is two-fold faster than in the presence of (3)-E. In the presence of a nonbioimprinted enzyme, esterification of (4) by (3)-C is five-fold faster than with (3)-E. The activity of bioimprinted (3)-E toward esterification of (4) is 4.5-fold higher than that of nonbioimprinted (3)-E. Switchable cyclic esterification of (4) is accomplished by sequential photoisomerization of the thiophenefulgide-modified α-chymotrypsin between states (3)-C and (3)-E.     

Verfeinerung der Kristallstruktur von Kupfer(II)-hydroxichlorid,Cu(OH)Cl

The crystal structure of Cu(OH)Cl [a=5.555 (2) Å,b=6.671 (4) Å,c=6.127 (2) Å, =114.88 (3)°, space group P2_I/a,Z=4] was refined for 810 observed reflections with sin /0.80 Å^–1 toR=0.035. Crystals were synthesized under hydrothermal conditions. The copper atom is planar four coordinated by three oxygen atoms and one chlorine atom; two further chlorine atoms complete its coordination. The copper polyhedra share edges to build up sheets, which are connected by hydrogen bonds to the chlorine atoms of adjacent sheets.

     

PbCu3(OH)(NO3)(SeO3)3·1/2H2O und Pb2Cu3O2(NO3)2(SeO3)2: Synthese und Kristallstrukturuntersuchung

Crystals of PbCu₃(OH)(NO₃)(SeO₃)₃·1/2H₂O [a=7.761(3)Å,b=9.478(4)Å,c=9.514(4)Å, =66.94(2)°, =69.83(2)°, =81.83(2)°, space group P ,Z=2] and Pb₂Cu₃O₂(NO₃)₂(SeO₃)₂ [a=5.884(2)Å,b=12.186(3)Å,c=19.371(4)Å, space group Cmc2₁,Z=4] were synthesized under hydrothermal conditions. Their crystal structures were refined with three-dimensional X-ray data toR _w=0.033 resp. 0.055. In PbCu₃(OH)(NO₃)(SeO₃)₃·1/2H₂O the Cu atoms are [4+1] and [4+2] coordinated and via SeO₃ groups a three-dimensional atomic arrangement is built up. In Pb₂Cu₃O₂(NO₃)₂(SeO₃)₂ there are sheets, which are connected only via Pb-O bonds ranging from 2.98 Å to 3.16 Å.

     

Crystal structure of NaCu5S3

The hexagonal compound NaCu₅S₃ [a=6.978 (5),c=7.209 (6) Å, space group P 6₃22-D ₆ ⁶ ,Z=2] was synthesized under hydrothermal conditions. The crystal structure was solved by direct methods from 140 single crystal X-ray data. The refinement yielded anR value of 2.3%. The Na atom has an octahedral coordination of S atoms [Na-S=2.89 Å, 6 ×]. The atom Cu(1) is bound to two S atoms at 2.19 Å and the atom Cu(2) to three atoms at 2.36 Å. In addition the Cu(1) atom is coordinated to four Cu(2) atoms, and the Cu(2) atom to six Cu(1) atoms with Cu-Cu distances of 2.70 Å and 2.72 Å. The S atom has an irregular coordination figure built up by two Na and four Cu atom neighbours. The connection of the different coordination polyhedra results in a framework structure.de|Die hexagonale Verbindung NaCu₅S₃ [a=6.978 (5),c=7.209 (6) Å, Raumgruppe P 6₃22-D ₆ ⁶ ,Z=2] wurde unter Hydrothermalbedingungen synthetisiert. Die Kristallstruktur wurde mittels direkter Methoden anhand von 140 Einkristall-Röntgendaten gelöst; die Verfeinerung ergab einenR-Wert von 2.3%. Das Na-Atom hat eine oktaedrische Koordination von S-Atomen [Na-S=2.89 Å, 6 ×]. Das Atom Cu(1) ist an zwei S-Atome mit 2.19 Å und das Atom Cu(2) an drei S-Atome mit 2.36 Å gebunden. Weiters wird das Atom Cu(1) von vier Cu(2)-Atomen und das Atom Cu(2) von sechs Cu(1)-Atomen umgeben, wobei die Cu-Cu-Abstände 2.70 Å und 2.72 Å betragen. Das S-Atom hat ein unregelmäßiges Koordinationspolyeder, das aus zwei Na- und vier Cu-Atomen aufgebaut wird. Die Verknüpfung dieser unterschiedlichen Koordinationspolyeder ergibt eine Gerüststruktur.

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Die Kristallstruktur von NaCu₅S₃

     

Enolethers. XXI. Synthesis of 5,5′-disubstituted 4,4′-bipyrimidines

1,6-Dialkoxy-3,4-diones 3 are easily accessible by acylation of enol ethers 1 with oxalyl chloride and subsequent elimination of hydrogen chloride using triethylamine. The open-chain 2,5-dimethyl derivative 3b is converted with amidines 4a-c and S-methylisothiourea (4d) , respectively, to give 2,2′-disubstituted 5,5′-dimethyl-4,4′-bipyrimidines 5a-d . The dihydrofuran and dihydropyran derivatives 3c and 3d , however, react with benzamidine (4c) in dimethylformamide only in the presence of calcium hydride as condensation agent yielding 5,5′-bis(2-hydroxyethyl)- and 5,5′-bis(3-hydroxypropyl)-2,2′-diphenyl-4,4′-bipyrimidine 6a and b.     

Oxidative Phosphonylation of Aromatic Compounds

Abstract

Aryl phosphonates can be prepared in good yields from the respective arenes and tri- or dialkylphosphites by either chemical or electrochemical oxidation^1. The anodic oxidation proceeds either via phosphonium radical cations which then attack the arenes electrophilically or via arene radical cations which add the trialkyl-phosphite as nucleophile^1,2. Aryl phosphonates are also obtained in good yields by chemical oxidation with peroxidisulfate/AgNO₃, Iron(III)- or Cerium(IV)-complexes in acetonitrile/water or glacial acetic acid^3.     

A convenient synthesis of optically active 5,5-disubstituted 4-amino- and 4-hydroxy-2(5H)-furanones from (S)-ketone cyanohydrins

(S)-Ketone cyanohydrins (S)-2 are accessible by enantioselective HCN addition to ketones 1 by using hydroxynitrile lyase from Manihot esculenta ((S)-MeHNL) as a biocatalyst. Acylation of (S)-2 gave the corresponding (S)-acyloxynitriles (S)-3, which can be cyclized by LHMDS to give 5,5-disubstituted (S)-4-amino-2(5H)-furanones (S)-4 and (S)-5. Different substituents (H. Me, OBn, OH) in the 3-position of the furanones were introduced by selecting the appropriate acylating agent, which in the case of benzyloxyacetyl chloride led to the novel structure type of 4-amino-3-hydroxyfuranones (S)-5. For the synthesis of 5,5-disubstituted (S)-tetronic acids (S)-8, ketone cyanohydrins (S)-2 were first transformed into the corresponding 2-hydroxy esters (S)-6. Acylation of (S)-6 gave 2-acyloxy esters (S)-7, which, by treatment with LHMDS or LDA, afforded tetronic acids (S)-8 in high yields and enantiomeric excesses. By debenzylation of benzyloxy acetoxy derivatives (S)-8e,f, the new vitamin C analogues (S)-9a,b were generated. All the described tetronic acid and aminofuranone derivatives were obtained in good chemical yields and without racemization with respect to the starting cyanohydrins (S)-2. In many cases the enantiomeric purity could be enriched by simple recrystallization (e.g. (S)-4a from 69% ee to > 99% ee).