Alois Steigel

Stereoregulation during the oligomerization of trityl methacrylate

Abstract For the first time, uniform optically active oligomers of methyl methacrylate with degrees of polymerization (DP) = 1, 2, 3, and 4 were obtained by the anionic polymerization of trityl methacrylate using 1,1-diphenylhexyl lithium/(−)sparteine, followed by the substitution of trityl for methyl, and subsequent g.p.c. separation. The mechanism for the formation of optically active poly(trityl methacrylate) is discussed in this paper.

Biotinylated Stealth® magnetoliposomes

Dimyristoylphosphatidylethanolamine (DC(14:0)PE) and the dioleoyl analogue (DC(18:1cis)PE) were mixed with alpha-biotinylamido-omega-N-succinimidoxycarbonyl-poly(ethylene glycol) (NHS-PEG-biotin) and quantitatively converted to alpha-biotinylamido-omega-(dimyristoylphosphatidylethanolamino-carbonyl)polyethylene glycol (DC(14:0)PE-PEG-biotin) and the dioleoyl analogue DC(18:1cis)PE-PEG-biotin, respectively. As shown by thin-layer chromatography and 1H NMR spectroscopy, PEGylation of both phosphatidylethanolamine types went to completion if the reaction was performed in organic solvent in the presence of triethylamine. The resulting derivatives were successfully incorporated into both classical phospholipid vesicles and a phospholipid bilayer surrounding nanometer-sized magnetite cores. In the latter case, the so-called activated Stealth(1) magnetoliposomes were produced which very efficiently immobilized streptavidinylated alkaline phosphatase.

Separation of retinoic acid all-trans, mono-cis and poly-cis isomers by reversed-phase high-performance liquid chromatography

Abstract An HPLC method using a reversed-phase Suplex-pKb-100 column that resolves photoisomerates of retinoic acid into nine peaks of products and the initial all- trans isomer is described. This separation is achieved with an isocratic mobile phase and a total elution time of ca . 95% of the products detected at 350 nm) sufficient for identification by proton NMR spectroscopy as mono- cis (9-, 11- and 13-) and di- cis (9,13- and 11,13-) isomers of retinoic acid were isolated using a protocol with two chromatographic steps. The methods described in this paper may prove of value in the study of retinoic acid isomer metabolism.

Combined chemoenzymatic synthesis of 20-6-deoxy-α-L-sorbofuranosyl-D-glucose

Abstract The chemoenzymatic synthesis of 20-6-deoxy-α-L-sorbofuranosyl-D-glucuse has been performed by coupling four enzymatic and one simple chemical step on a preparative scale with 17% overall yield. At first, pyruvic aldehyde dimethyl acetal was reduced stereospecifically to L-lactaldehyde dimethyl acetal by the carbonyl reductase from Candida parapsilosis with approximately 100% ee. Subsequently, the product was converted to L-lactaldehyde by simple treatment with a strong cation exchanger. Secondly, stereoselective condensation between dihydroxyacetone phosphate and L-lactaldehyde was catalyzed by fructose 1,6-bisphosphate aldolase from Staphylococcus carnosus. The resulting sugar phosphate was dephosphorylated by acid phosphatase treatment and further purified by cation exchange chromatography. The structure and stereochemistry of the product, 6-deoxy-L-sorbose, was confirmed by 1H- and 13C-NMR analysis. In the last step sucrose synthase from rice grains was utilized to catalyze the transfer of glucose from UDP-glucose to 6-deoxy-L-sorbose. The structure and stereochemistry of the disaccharide formed, 20-6-deoxy-a-L-sorbofuranosyl-D-glucose, was also confirmed by 1H- and 13C-NMR analysis.

Analysis of the stereochemistry of poly(2,3-epoxypropyl methacrylate) by 75 MHz 13C n.m.r. spectroscopy

Abstract The tacticity of poly(2,3-epoxypropyl methacrylate) has been analysed. For detailed elucidation of stereochemical features, polymers with varying degrees of tacticities were synthesized by anionic and free radical polymerization. Using two-dimensional 13C1H correlation, signal assignments to different carbon atoms have been made. Using the peak multiplicities for carbonyl carbon atom resonance, in particular, tacticity assignments up to the pentad level have been achieved. The validity of sequence assignments has been tested and confirmed by calculated values from statistical relationships. While the anionically polymerized sample in toluene obeys a first-order Markov type chain growth process, the chain propagation for free radical polymer and anionic polymer in THF has been found to be Bernoullian.

Dihydrodiazatropone aus cyclobutenonen und diazoalkanen

Abstract The cycloaddition of diazoalkanes to cyclobutenones proves to be a useful access to diazatropone derivatives.

Diacetoxy-substituted polyacetylenes from Atractylodes lancea

Abstract Six new polyacetylenes have been isolated from the rhizomes of Atractylodes lancea . Besides 1-(2-furyl)-(7 E )-nonene-3,5-diyne-1,2-diacetate, a new natural compound, two further vicinal diacetoxyalkenynes were postulated as erythro- and threo -forms of (1,5 E , 11 E )-tridecatriene-7,9-diyne-3,4-diacetate in comparison with similar structures in the literature. Three other constituents turned out to be (3 E ,5 E ,11 E )-tridecatriene-7,9-diyne-1,2-diacetate together with its (3 Z )- and (5 Z )-isomers. All structures were established by UV, EI-mass spectrometry, 1D and 2D NMR experiments.

4,5-Dihydro-1H-azepine aus aktivierten Cyclobutenen und 1,3-Dipolen

Cycloaddition of diphenylnitrile ylide to dicyanocyclobutene and of a mesoionic oxazolium-5-olate to isopropylidenecyclobutenone yields dihydroazepine derivatives by cleavage of the strained internal σ-bonds in the primarily formed bicyclic adducts.

Syn-anti selectivity of cis-3,4-disubstituted cyclobutenes : Part 3: Chloro-thio- and Dithio-substituted Cyclobutenes☆

Cycloadditions of the 3.4-substituted cyclobutenes L, M with diazoalkanes RR′CN2, R = H und R′ = H, alkyl, aryl or alkoxycarbonyl exclusively yield syn-adducts. Diphenylnitrilimine and mesitonitrile oxide mainly undergo anti-addition.

Fructose-1,6-Bisphosphate Aldolases from Staphylococcus Carnosus: Stereoselective Enzymatic Synthesis of Ketose-1-Phosphates and Successive Reaction to 1,3-Dioxanes

During the enzymatic synthesis of open chain ketose-1-phosphates on a preparative scale using fructose-1,6-bisphosphate aldolases from Staphylococcus carnosus a successive reaction of excess aldehyde with the primary reaction product was observed leading to the corresponding 1,3-dioxane derivatives. The thermodynamic equilibrium between aldehyde, ketose-1-phosphate and the 1,3-dioxane derivative was studied. It could be demonstrated that the enzyme is not required for the successive reaction of 2-methylpropanol or propanal with 5,6-dideoxy-5-methyl-D-threo-hexulose-1-phospate yielding the semiacetal, but the reaction rate is considerably faster and yields of 2,6-bis-(1-methylethyl)-4,5-dihydroxy-4-phosphorylmethyl-1,3-dioxane are higher if the reaction starts with dihydroxyacetone-phosphate and 2-methylpropanal in the presence of the aldolase. 1,3-dioxane formation was not observed in the enzymatic synthesis of 6-deoxy-L-sorbose-1-phosphate using a high excess of L-lactaldehyde, which was attributed to the kinetically favored cyclisation to the furanose form in water.