| 1. |
- Bergman, Jan, et al.
(författare)
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Acid-induced dimerization of 3-(1H-indol-3-yl)maleimides. Formation of cyclopentindole derivatives
- 2000
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Ingår i: JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 1. - : Royal Society of Chemistry (RSC). - 1470-4358 .- 1364-5463 .- 1472-7781. ; :16, s. 2615-2621
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Tidskriftsartikel (refereegranskat)abstract
- Acid-induced dimerizations of 3-substituted maleimides have been investigated, leading to e.g. the cyclopentindole 9 and the deeply coloured spiro compounds 24 and 25 in good yields. 3-(1H-Indol-3-yl)maleimide 6b readily gave the cycloaddition products 13-15 on treatment with appropriate dienophiles. In addition, several related 3,3-di-(1H-indol-3-yl)succinimides have been prepared and studied.
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| 2. |
- Bergman, Jan, et al.
(författare)
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Coupling reactions of indole-3-acetic acid derivatives. Synthesis of arcyriaflavin A
- 2000
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Ingår i: JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 1. - : Royal Society of Chemistry (RSC). - 1470-4358 .- 1364-5463 .- 1472-7781. ; :16, s. 2609-2614
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Tidskriftsartikel (refereegranskat)abstract
- The bisindolesuccinic acid methyl ester 10 was obtained by an iodine-promoted coupling of the dianion 9. The diester was converted to the N-benzylimide 12, which was oxidatively cyclized to the indolo[2,3-a]pyrrolo[3,4-c]carbazole 15. The diester 10 could be directly transformed to the known indolocarbazole diester 27 via acid-induced intramolecular cyclization in TFA. The same methodology gave arcyriaflavin A 4 from the succinimide 18b.
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| 3. |
- Bhattacharyya, Sumita, et al.
(författare)
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The p-methoxybenzyl ether as an in situ-removable carbohydrate-protecting group : A simple one-pot synthesis of the globotetraose tetrasaccharide
- 2001
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Ingår i: Journal of the Chemical Society - Perkin Transactions 1. - : Royal Society of Chemistry (RSC). - 1472-7781 .- 1364-5463. ; :8, s. 886-890
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Tidskriftsartikel (refereegranskat)abstract
- A one-pot synthesis of the globotetraose tetrasaccharide is reported. The synthetic method relies on the use of a p-methoxybenzyl ether as an in situ-removable protecting group. N-Iodosuccinimide/trifluoromethanesulfonic acid-promoted glycosylation of 2-bromoethyl-2,3,6-tri-O-benzoyl-4-O-(2,3,6-tri-O-benzoyl-β-D-galactopyranosyl)-β-D-glucopyranoside 5 at −45 °C with phenyl 2,4,6-tri-O-benzyl-3-O-(4-methoxybenzyl)-1-thio-β-D-galactopyranoside 6 gives an intermediate trisaccharide from which the p-methoxybenzyl ether is removed by allowing the reaction temperature to rise to 0 °C for 40 min. Again lowering the temperature to −45 °C, followed by addition of methyl 3,4,6-tri-O-acetyl-2-trichloroethoxycarbonylamino-2-deoxy-1-thio-β-D-galactopyranoside 8, affords the globotetraose tetrasaccharide 11 in one-pot in an excellent yield of 76%.
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| 4. |
- Botes, AL, et al.
(författare)
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Screening of yeast species for the stereo-selective reduction of bicyclo[2.2.2]octane-2,6-dione
- 2002
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Ingår i: Journal of the Chemical Society - Perkin Transactions 1. - : Royal Society of Chemistry (RSC). - 1472-7781 .- 1364-5463. ; :8, s. 1111-1114
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Tidskriftsartikel (refereegranskat)abstract
- Yeast strains from more than 31 different genera were screened for the enantioselective reduction of bicyclo[2.2.2]-octane-2,6-dione (1). Reducing activity was found in 80% of the screened yeasts. Bicyclo[2.2.2]octane-2,6-dione was enantioselectively reduced (> 98% ee) to (1R, 4S, 6S)-6-hydroxybicyclo[2.2.2]octane-2-one (-)-2 by 69% of the strains. Enantioselective reduction of the diketone to (1S, 4R, 6S)-6-hydroxybicyclo[2.2.2]octane-2-one ((+)-3, >98% ee) as a major product is reported for the first time. Candida tropicalis UOFS Y-0534 and Candida wickerhamii UOFS Y-0652 displayed this unusual diastereoselectivity.
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| 5. |
- George, Shaji K, et al.
(författare)
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Chemoenzymatic synthesis of derivatives of a T-cell-stimulating peptide which carry tumor-associated carbohydrate antigens
- 2001
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Ingår i: Journal of the Chemical Society-Perkin Transactions 1. - : Royal Society of Chemistry (RSC). - 1472-7781 .- 1364-5463. ; , s. 880-5
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Tidskriftsartikel (refereegranskat)abstract
- The Tn (GalNAc-Ser/Thr), T [Gal(13)GalNAc-Ser/Thr], sialyl-Tn [Neu5Ac(26)GalNAc-Ser/Thr] and 2,3-sialyl-T [Neu5Ac(23)Gal(13)GalNAc-Ser/Thr] antigens are examples of tumor-associated carbohydrate antigens expressed by epithelial cancers. We now describe the preparation of 2-bromoethyl glycosides corresponding to the Tn and T antigens in one and five chemical steps (51 and 15% total yield), respectively, starting from N-acetylgalactosamine. The 2-bromoethyl Tn and T glycosides were used to alkylate a homocysteine residue incorporated in a peptide that is able to bind to class I MHC molecules on antigen-presenting cells. The two neoglycopeptides were then converted into glycopeptides which carry the sialyl-Tn and 2,3-sialyl-T antigens by using recombinant sialyltransferases. Interestingly, the sialyltransferases were able to sialylate the Tn and T carbohydrate moieties even though they were linked to the peptide backbone via a spacer instead of being attached to serine or threonine. The four glycopeptides will be used in studies directed towards inducing a carbohydrate-specific T cell response against the Tn, T, sialyl-Tn, and 2,3-sialyl-T antigens.
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| 6. |
- Gustafsson, Magnus, et al.
(författare)
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The effect of oxygen on the regioselectivity in the rhodium catalysed hydrosilylation of 1,3-dienes
- 2002
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Ingår i: Journal of the Chemical Society - Perkin Transactions 1. - : Royal Society of Chemistry (RSC). - 1472-7781 .- 1364-5463. ; :1, s. 102-107
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Tidskriftsartikel (refereegranskat)abstract
- The regioselectivity of the hydrosilylation of substituted 1,3-dienes catalysed by several rhodium complexes in the presence and absence of oxygen was studied. In addition to the already known accelerating effect, the presence of oxygen strongly affected the product distribution. For 2-substituted 1,3-dienes in the presence of oxygen the regioselectivity was in the range of 1 : 6 to 1 : 10 in favour of the head-product, while the absence of oxygen changed the ratios to 1 : 1 to 3 : 1 in fa our of the tail-product. When HSiPh3 was used in the presence of oxygen a single isomer was isolated in 87% yield, while in the absence of oxygen a mixture of products was produced. Control experiments indicated that a heterogeneous/colloidal catalytic system may be responsible for the preferred head-product formation.
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| 7. |
- Hedenström, Erik, et al.
(författare)
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Synthesis and lipase catalysed stereoselective acylation of some 3-methyl-2-alkanols, identified as sex pheromone precursors in females of pine sawfly species
- 2002
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Ingår i: Journal of The Chemical Society, Perkin Transactions 1. - : Royal Society of Chemistry (RSC). - 1472-7781. ; 2002:15, s. 1810-1817
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Tidskriftsartikel (refereegranskat)abstract
- Several 3-methylalkan-2-ols precursors to sex pheromones of Diprion pini, Gilpinia pallida, Gilpinia frutetorum, Diprion nipponica, Macrodiprion nemoralis and Microdiprion pallipes were synthesised as stereoisomeric mixtures in moderate to good yields. The key reaction sequence in the syntheses was the ring opening of either cis- or racemic trans-epoxybutane using a higher order cyanocuprate as nucleophile followed by a highly efficient lipase catalysed stereoselective acylation of the obtained 3-methylalkan-2-ol. The biologically active species specific stereoisomer was synthesised as a single stereoisomer in high stereoisomeric purity, as one in a mixture of two or as one of four stereoisomers when the appropriate 3-methylalkan-2-ol was stereoselectively acylated using a Pseudomonas sp. lipase as catalyst.
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| 8. |
- Hedenström, Erik, et al.
(författare)
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Synthesis of N-propionylated (S)-(-)-2-(pyrrolidin-2-yl)propan-2-ol and its use as a chiral auxiliary and selectivity marker in asymmetric aldol reactions
- 2000
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Ingår i: Journal of the Chemical Society. Perkin Transactions 1. - : Royal Society of Chemistry (RSC). - 1472-7781 .- 1470-4358 .- 1364-5463. ; 2000, s. 1513-1518
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Tidskriftsartikel (refereegranskat)abstract
- The N-propionylated pyrrolidine derivative and chiral auxiliary, (S)-(-)-2-(pyrrolidin-2-yl)propan-2-ol, was synthesised and used in stereoselective aldol reactions with benzaldehyde. Differences in stereoselectivity were investigated as a function of temperature, solvent, chelating agent and the amount of the chelating agent used by monitoring the 1H NMR spectra of the aldol adducts that were obtained. Among the additives that were investigated, Cp2ZrCl2 induced higher syn-selectivity, while SnCl2 induced higher syn-selectivity respectively. TMSCl was found to induce high selectivity for one syn- and one anti-diastereomer. Varying the ligand sets on titanium additives was found to induce differences in selectivity, with (i-PrO)3TiCl exhibiting syn-selectivity and Cp2TiCl2 exhibiting anti-selectivity. Differences in reactivity and stereoselectivity were also found to depend upon the amount of Lewis acid that was added. Methods for removal of the auxiliary were also investigated. Acidic hydrolysis was used successfully to obtain the desired 3-hydroxy-2-methyl-3-phenylpropionic acids, but was found to give low yields and resulted in a large amount of epimerisation. Furthermore, the ethyl esters of these hydroxy acids are easy to separate into pure syn- and anti-diastereomers by LC. © The Royal Society of Chemistry 2000.
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| 9. |
- Janosik, Tomasz, et al.
(författare)
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Thionation of bisindole derivatives with P4S10 or elemental sulfur
- 2002
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Ingår i: Journal of the Chemical Society - Perkin Transactions 1. - : Royal Society of Chemistry (RSC). - 1472-7781 .- 1364-5463. ; :3, s. 330-334
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Tidskriftsartikel (refereegranskat)abstract
- Thionation reactions of several bisindole derivatives using elemental sulfur or P4S10 in pyridine have been studied, leading to formation of several novel structures. The reaction of indigo or isatin with P4S10 gave the structurally new salt 10, which could be transformed into the ethyl derivative 11. The first example of a thionated indigo derivative, monothioindigo (6), was isolated in low yield from the thionation of isatin. Treatment of 3,3'-biindolyl with sulfur in hot DMF produced the previously known tetrasulfide 1, which was studied by X-ray crystallography, thus also establishing that 1 is chiral in the crystalline state. The structure of an additional thionation product, the thienoindole derivative 34 was also solved using X-ray crystallography.
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| 10. |
- Karlsson, Staffan, et al.
(författare)
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Diastereoselective addition of chiral azomethine ylides to cyclic alpha,beta-unsaturated N-enoylbornanesultams
- 2002
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Ingår i: Journal of the Chemical Society. Perkin Transactions 1. - : Royal Society of Chemistry (RSC). - 1472-7781 .- 1364-5463. ; 2002:8, s. 1076-1081
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Tidskriftsartikel (refereegranskat)abstract
- Doubly diastereoselective 1,3-dipolar cycloaddition reactions of chiral non-racemic azomethine ylides to cyclic five-and six-membered α,β-unsaturated N-enoylbornanesultams were carried out. When suitable solvents were used, the fused bicyclic adducts formed were obtained in good diastereoselectivity. Moreover, a change of the absolute configuration of the starting ylide precursor reversed the diastereoselectivity of some such reactions. Cleavage of the chiral auxiliary of the cycloadducts furnished amino alcohols and a β-amino ester. The latter was transformed into a known precursor of an antibacterial compound.
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