Karl Hult | KTH Royal Institute of Technology (original) (raw)
Papers by Karl Hult
Acta Chem Scand, 1996
Reaction of 3,4,6-tri-O-acetyl-beta-D-glucopyranosyl chloride (1) with potassium phenylselenate g... more Reaction of 3,4,6-tri-O-acetyl-beta-D-glucopyranosyl chloride (1) with potassium phenylselenate gave phenyl 3,4,6-tri-O-acetyl-1-seleno-alpha, beta-D-glucopyranoside (2) in 59% yield. Silylation of benzyl 3,4,6-tri-O-benzyl-beta-D-glucopyranoside (4) with ethyl 3,4,6-tri-O-benzyl-2-O-chlorodimethylsilyl-1-thio-beta -D-glucopyranoside gave benzyl 2-O-(3,4, 6-tri-O-benzyl-1-S-ethyl-1-thio-beta-D-glucopyranos-2-O-yldimet hylsilyl)-3,4,6,-tri-O-benzyl-beta-D-glucopyranoside (5) in 35% yield. Reaction of 5 with N-iodosuccinimide in nitromethane gave benzyl 2-O-(3,4, 6-tri-O-benzyl-alpha-D-glucopyranosyl)-3,4, 6-tri-O-benzyl-beta-D-glucopyranoside (6) in 45% yield. Chlorodimethylsilylation of phenyl 3,4, 6-tri-O-acetyl-1-seleno-alpha-D-glucopyranoside (2 alpha) and reaction with 6 gave benzyl 2-O-[2-O-(3,4,6 -tri-O-acetyl-1-Se-phenyl-1-seleno-alpha-D-glucopyranos-2-O-yld imethylsilyl) -3,4,6-tri-O-benzyl-alpha-D-glucopyranosyl]-3,4,6-tri-O-benzyl-beta-D- glucopyranoside (7) in 82% yield. Intramolecular glycosidation of 7 using N-iodosuccinimide in nitromethane gave benzyl 2-O-[2-O-(3,4,6-tri-O-acetyl-alpha-D-glucopyranosyl)-3, 4,6-tri-O-benzyl-alpha-D-glucopyranosyl]-3, 4,6-tri-O-benzyl-beta-D-glucopyranoside (8) in 45% yield. Deprotection of 8 gave kojitriose (9) in quantitative yield. Chlorodimethylsilylation of 1,3,4,6-tetra-O-benzyl-alpha, beta-D-fructofuranose (10) with dimethyldichlorosilane and pyridine followed by reaction with ethyl 3,4, 6-tri-O-benzyl-1-thio-beta-D-glucopyranoside (3) gave ethyl 2-O-(1,3,4,6-tetra-O-benzyl-alpha, beta-D-fructofuranosyloxydimethylsilyl)-3,4, 6-tri-O-benzyl-1-thio-beta-D-glucopyranoside (11) in 85% yield. Chlorodimethylsilylation of 1,3,4, 6-tetra-O-benzoyl-alpha-D-fructofuranose (12) with dimethyldicholorosilane and triethylamine followed by reaction with phenyl 3,4, 6-tri-O-acetyl-1-thio-alpha-D-glucopyranoside (13) gave phenyl 2-O-(1,3,4, 6-tetra-O-benzoyl-alpha-D-fructofuranosyloxydimethylsilyl)-3, 4,6-tri-O-acetyl-1-thio-alpha-D-glucopyranoside (14) in 62% yield. Both 11 and 14 failed to undergo intramolecular glycosidation.
Chembiochem, 2010
The size of the stereoselectivity pocket of Candida antarctica lipase B limits the range of alcoh... more The size of the stereoselectivity pocket of Candida antarctica lipase B limits the range of alcohols that can be resolved with this enzyme. These steric constrains have been changed by increasing the size of the pocket by the mutation W104A. The mutated enzyme has good activity and enantioselectivity toward bulky secondary alcohols, such as 1-phenylalkanols, with alkyl chains up to eight carbon atoms. The S enantiomer was preferred in contrast to the wild-type enzyme, which has R selectivity. The magnitude of the enantioselectivity changes in an interesting way with the chain length of the alkyl moiety. It is governed by interplay between entropic and enthalpic contributions and substrates with long alkyl chains are resolved best with E values higher than 100. The enantioselectivity increases with temperature for the small substrates, but decreases for the long ones.
Journal of Molecular Catalysis B Enzymatic, Dec 1, 2004
A Ser105Ala mutant of Candida antarctica lipase B has previously been shown to catalyze aldol add... more A Ser105Ala mutant of Candida antarctica lipase B has previously been shown to catalyze aldol additions. Quantum chemical calculations predicted a reaction rate similar to that of natural enzymes, whereas experiments showed a much lower reaction rate. Molecular dynamics simulations, presented here, show that the low reaction rate is a consequence of the low frequencies of near attack complexes in
Nat Toxins, 1998
The natural occurrence of ochratoxin A in grain samples of 23 rice cultivars was in the range 0.0... more The natural occurrence of ochratoxin A in grain samples of 23 rice cultivars was in the range 0.01±1.0 ng g À1 rice. Samples from the same cultivars were surface sterilized with NaClO, dried to 19 % water content and equilibrated at water activity (a w ) 0.75 and 20°C for 8 days. Varietal differences in equilibrium w/w water content (p`0.0001) were found, re¯ected by differences in amylose and protein contents. Samples were then inoculated with an isolate of Penicillium verrucosum with 1 ml spore suspension to each 50 g rice sample; and incubated at a w 0.75 and 20°C for 23 weeks. During incubation, ochratoxin A was accumulated in all cultivars. Signi®cant varietal differences in ochratoxin A accumulation were observed (p`0.0001). Grain samples with less than 19.5 % equilibrium water content accumulated less ochratoxin A (p`0.005). In a multiple regression analysis accumulated ochratoxin A content was expressed as a function of natural occurrence of ochratoxin A (p`0.05), equilibrium water content at time of inoculation (p`0.005), 1000-grain weight (p`0.1), and chalkiness of endosperm (p`0.05), with p`0.0001 for the full function. Naturally occurring ochratoxin A was the strongest independent variable with p`0.0005 for the slope coef®cient in single regression. Rice cultivars IR8, IR24, IR620030-18-2-2 and R91-1081-1 had exceptionally low accumulation of ochratoxin A. . ln(area), natural logarithm of accumulater ochratoxin A over time; Equ. water, equilibrium water content w/w, %; Amylose and Am, amylose content, % of tot starch; Protein and Prot = crude protein content, % (N%x6.25); 1000-w = weight of 1000 kernels, g; Nat. occ. = natural occurrence of ochratoxin A, ng g À1 rice; Chalk, chalkiness of endosperm, waxy, 0, 1, 5, 9. Number of grains out of 200. infected by: Asp = Aspergillus sp. Cur = Curvularia sp. Fm = Fusarium sp. N = Nigrospora sp.
Applied and Environmental Microbiology
At a number of slaughters nephropathy and high ochratoxin A contents in kidneys have been observe... more At a number of slaughters nephropathy and high ochratoxin A contents in kidneys have been observed in fattening pigs from two Swedish farms. In one herd the source of contamination was barley grown on the home farm and stored under such conditions that the growth of fungal species (Penicillium verrucosum var. verrucosum) producing ochratoxin A occurred, with the subsequent formation of the toxin. In this case high ochratoxin A levels in fattening pigs were found during a period of about 18 months. In the second herd, where compounded feed was used, it was impossible to locate the source of contamination. It was presumed that a consignment of feed was damaged by rain during storage at the farm. Ochratoxin A was found in fattening pigs from this herd for a period of about 2 months. Ochratoxin A appeared in the kidneys of all investigated pigs. In some animals the livers, whole blood, and plasma were analyzed, too. The livers contained somewhat lower amounts of ochratoxin A than the kidneys, whereas the content in whole blood and plasma, respectively, was 5 and 13 times greater. Kidneys spontaneously contaminated with ochratoxin A, when stored for 10 months at -70°C, showed no systematic decrease in toxin content.
Applied and Environmental Microbiology
Samples of pig blood, intended for ochratoxin A analysis, were collected from pigs of 279 randoml... more Samples of pig blood, intended for ochratoxin A analysis, were collected from pigs of 279 randomly selected herds. The samples were obtained at nine different slaughterhouses from different areas of Sweden. Pigs from 47 herds (16.8% of the total) exhibited ochratoxin A in amounts of greater than or equal to 2 ng of ochratoxin A per ml of blood. One sample each from a single pig per herd identified herds contaminated with ochratoxin A in amounts exceeding three times the detection limit of the method (3 x 2 ng of ochratoxin A per ml of blood = 6 ng of ochratoxin A per ml of blood). There was a good agreement between ochratoxin A concentrations in the blood from different pigs within the same herd (correlation coefficient = 0.80). The ochratoxin A concentration in pig blood was used as an estimate of the ochratoxin A content of the consumed feed. This method showed that feed from grain produced on-farm contained higher concentrations of ochratoxin A than commercial feed preparations. No geographical variation of ochratoxin A occurrence within Sweden was detected.
Applied and Environmental Microbiology
The fate of ochratoxin A during incubation with contents from the four stomachs of the cow was st... more The fate of ochratoxin A during incubation with contents from the four stomachs of the cow was studied. It was concluded that ochratoxin A was cleaved into the nontoxic ochratoxin alpha and phenylalanine by the contents from all but the abomasum.
found at: Updated information and services can be These include: CONTENT ALERTS more» alerts (whe... more found at: Updated information and services can be These include: CONTENT ALERTS more» alerts (when new articles cite this article), Receive: RSS Feeds, eTOCs, free email http://journals.asm.org/site/misc/reprints.xhtml Information about commercial reprint orders: http://journals.asm.org/site/subscriptions/ To subscribe to to another ASM Journal go to: on June 9, 2013 by guest
Journal - Association of Official Analytical Chemists
ABSTRACT
Applied and Environmental Microbiology
A procedure is presented for screening the quality of feed in respect to ochratoxin A contaminati... more A procedure is presented for screening the quality of feed in respect to ochratoxin A contamination based upon the analysis of ochratoxin A in pig blood. Representative samples from large feed lots may be obtained by using pigs as in vivo sample collectors which enrich the toxin and forms homogeneous samples in the blood. The spectrofluorometric procedure for ochratoxin A analysis (K. Hult and S. Gatenbeck, J. Assoc. Off. Anal. Chem. 59:128-129, 1976) has been adapted to pig blood and has been simplified to involve only three extraction steps. A volume of 2.5 ml of blood or plasma is needed, and the detection limit is 2 ng of ochratoxin A per ml. The disappearance of ochratoxin A from pig blood as a function of time has been studied. A feeding experiment with ochratoxin A has been performed, and the time course of the concentration of ochratoxin A in blood has been followed during the experiment.
Acta Chem Scand, 1996
Reaction of 3,4,6-tri-O-acetyl-beta-D-glucopyranosyl chloride (1) with potassium phenylselenate g... more Reaction of 3,4,6-tri-O-acetyl-beta-D-glucopyranosyl chloride (1) with potassium phenylselenate gave phenyl 3,4,6-tri-O-acetyl-1-seleno-alpha, beta-D-glucopyranoside (2) in 59% yield. Silylation of benzyl 3,4,6-tri-O-benzyl-beta-D-glucopyranoside (4) with ethyl 3,4,6-tri-O-benzyl-2-O-chlorodimethylsilyl-1-thio-beta -D-glucopyranoside gave benzyl 2-O-(3,4, 6-tri-O-benzyl-1-S-ethyl-1-thio-beta-D-glucopyranos-2-O-yldimet hylsilyl)-3,4,6,-tri-O-benzyl-beta-D-glucopyranoside (5) in 35% yield. Reaction of 5 with N-iodosuccinimide in nitromethane gave benzyl 2-O-(3,4, 6-tri-O-benzyl-alpha-D-glucopyranosyl)-3,4, 6-tri-O-benzyl-beta-D-glucopyranoside (6) in 45% yield. Chlorodimethylsilylation of phenyl 3,4, 6-tri-O-acetyl-1-seleno-alpha-D-glucopyranoside (2 alpha) and reaction with 6 gave benzyl 2-O-[2-O-(3,4,6 -tri-O-acetyl-1-Se-phenyl-1-seleno-alpha-D-glucopyranos-2-O-yld imethylsilyl) -3,4,6-tri-O-benzyl-alpha-D-glucopyranosyl]-3,4,6-tri-O-benzyl-beta-D- glucopyranoside (7) in 82% yield. Intramolecular glycosidation of 7 using N-iodosuccinimide in nitromethane gave benzyl 2-O-[2-O-(3,4,6-tri-O-acetyl-alpha-D-glucopyranosyl)-3, 4,6-tri-O-benzyl-alpha-D-glucopyranosyl]-3, 4,6-tri-O-benzyl-beta-D-glucopyranoside (8) in 45% yield. Deprotection of 8 gave kojitriose (9) in quantitative yield. Chlorodimethylsilylation of 1,3,4,6-tetra-O-benzyl-alpha, beta-D-fructofuranose (10) with dimethyldichlorosilane and pyridine followed by reaction with ethyl 3,4, 6-tri-O-benzyl-1-thio-beta-D-glucopyranoside (3) gave ethyl 2-O-(1,3,4,6-tetra-O-benzyl-alpha, beta-D-fructofuranosyloxydimethylsilyl)-3,4, 6-tri-O-benzyl-1-thio-beta-D-glucopyranoside (11) in 85% yield. Chlorodimethylsilylation of 1,3,4, 6-tetra-O-benzoyl-alpha-D-fructofuranose (12) with dimethyldicholorosilane and triethylamine followed by reaction with phenyl 3,4, 6-tri-O-acetyl-1-thio-alpha-D-glucopyranoside (13) gave phenyl 2-O-(1,3,4, 6-tetra-O-benzoyl-alpha-D-fructofuranosyloxydimethylsilyl)-3, 4,6-tri-O-acetyl-1-thio-alpha-D-glucopyranoside (14) in 62% yield. Both 11 and 14 failed to undergo intramolecular glycosidation.
Chembiochem, 2010
The size of the stereoselectivity pocket of Candida antarctica lipase B limits the range of alcoh... more The size of the stereoselectivity pocket of Candida antarctica lipase B limits the range of alcohols that can be resolved with this enzyme. These steric constrains have been changed by increasing the size of the pocket by the mutation W104A. The mutated enzyme has good activity and enantioselectivity toward bulky secondary alcohols, such as 1-phenylalkanols, with alkyl chains up to eight carbon atoms. The S enantiomer was preferred in contrast to the wild-type enzyme, which has R selectivity. The magnitude of the enantioselectivity changes in an interesting way with the chain length of the alkyl moiety. It is governed by interplay between entropic and enthalpic contributions and substrates with long alkyl chains are resolved best with E values higher than 100. The enantioselectivity increases with temperature for the small substrates, but decreases for the long ones.
Journal of Molecular Catalysis B Enzymatic, Dec 1, 2004
A Ser105Ala mutant of Candida antarctica lipase B has previously been shown to catalyze aldol add... more A Ser105Ala mutant of Candida antarctica lipase B has previously been shown to catalyze aldol additions. Quantum chemical calculations predicted a reaction rate similar to that of natural enzymes, whereas experiments showed a much lower reaction rate. Molecular dynamics simulations, presented here, show that the low reaction rate is a consequence of the low frequencies of near attack complexes in
Nat Toxins, 1998
The natural occurrence of ochratoxin A in grain samples of 23 rice cultivars was in the range 0.0... more The natural occurrence of ochratoxin A in grain samples of 23 rice cultivars was in the range 0.01±1.0 ng g À1 rice. Samples from the same cultivars were surface sterilized with NaClO, dried to 19 % water content and equilibrated at water activity (a w ) 0.75 and 20°C for 8 days. Varietal differences in equilibrium w/w water content (p`0.0001) were found, re¯ected by differences in amylose and protein contents. Samples were then inoculated with an isolate of Penicillium verrucosum with 1 ml spore suspension to each 50 g rice sample; and incubated at a w 0.75 and 20°C for 23 weeks. During incubation, ochratoxin A was accumulated in all cultivars. Signi®cant varietal differences in ochratoxin A accumulation were observed (p`0.0001). Grain samples with less than 19.5 % equilibrium water content accumulated less ochratoxin A (p`0.005). In a multiple regression analysis accumulated ochratoxin A content was expressed as a function of natural occurrence of ochratoxin A (p`0.05), equilibrium water content at time of inoculation (p`0.005), 1000-grain weight (p`0.1), and chalkiness of endosperm (p`0.05), with p`0.0001 for the full function. Naturally occurring ochratoxin A was the strongest independent variable with p`0.0005 for the slope coef®cient in single regression. Rice cultivars IR8, IR24, IR620030-18-2-2 and R91-1081-1 had exceptionally low accumulation of ochratoxin A. . ln(area), natural logarithm of accumulater ochratoxin A over time; Equ. water, equilibrium water content w/w, %; Amylose and Am, amylose content, % of tot starch; Protein and Prot = crude protein content, % (N%x6.25); 1000-w = weight of 1000 kernels, g; Nat. occ. = natural occurrence of ochratoxin A, ng g À1 rice; Chalk, chalkiness of endosperm, waxy, 0, 1, 5, 9. Number of grains out of 200. infected by: Asp = Aspergillus sp. Cur = Curvularia sp. Fm = Fusarium sp. N = Nigrospora sp.
Applied and Environmental Microbiology
At a number of slaughters nephropathy and high ochratoxin A contents in kidneys have been observe... more At a number of slaughters nephropathy and high ochratoxin A contents in kidneys have been observed in fattening pigs from two Swedish farms. In one herd the source of contamination was barley grown on the home farm and stored under such conditions that the growth of fungal species (Penicillium verrucosum var. verrucosum) producing ochratoxin A occurred, with the subsequent formation of the toxin. In this case high ochratoxin A levels in fattening pigs were found during a period of about 18 months. In the second herd, where compounded feed was used, it was impossible to locate the source of contamination. It was presumed that a consignment of feed was damaged by rain during storage at the farm. Ochratoxin A was found in fattening pigs from this herd for a period of about 2 months. Ochratoxin A appeared in the kidneys of all investigated pigs. In some animals the livers, whole blood, and plasma were analyzed, too. The livers contained somewhat lower amounts of ochratoxin A than the kidneys, whereas the content in whole blood and plasma, respectively, was 5 and 13 times greater. Kidneys spontaneously contaminated with ochratoxin A, when stored for 10 months at -70°C, showed no systematic decrease in toxin content.
Applied and Environmental Microbiology
Samples of pig blood, intended for ochratoxin A analysis, were collected from pigs of 279 randoml... more Samples of pig blood, intended for ochratoxin A analysis, were collected from pigs of 279 randomly selected herds. The samples were obtained at nine different slaughterhouses from different areas of Sweden. Pigs from 47 herds (16.8% of the total) exhibited ochratoxin A in amounts of greater than or equal to 2 ng of ochratoxin A per ml of blood. One sample each from a single pig per herd identified herds contaminated with ochratoxin A in amounts exceeding three times the detection limit of the method (3 x 2 ng of ochratoxin A per ml of blood = 6 ng of ochratoxin A per ml of blood). There was a good agreement between ochratoxin A concentrations in the blood from different pigs within the same herd (correlation coefficient = 0.80). The ochratoxin A concentration in pig blood was used as an estimate of the ochratoxin A content of the consumed feed. This method showed that feed from grain produced on-farm contained higher concentrations of ochratoxin A than commercial feed preparations. No geographical variation of ochratoxin A occurrence within Sweden was detected.
Applied and Environmental Microbiology
The fate of ochratoxin A during incubation with contents from the four stomachs of the cow was st... more The fate of ochratoxin A during incubation with contents from the four stomachs of the cow was studied. It was concluded that ochratoxin A was cleaved into the nontoxic ochratoxin alpha and phenylalanine by the contents from all but the abomasum.
found at: Updated information and services can be These include: CONTENT ALERTS more» alerts (whe... more found at: Updated information and services can be These include: CONTENT ALERTS more» alerts (when new articles cite this article), Receive: RSS Feeds, eTOCs, free email http://journals.asm.org/site/misc/reprints.xhtml Information about commercial reprint orders: http://journals.asm.org/site/subscriptions/ To subscribe to to another ASM Journal go to: on June 9, 2013 by guest
Journal - Association of Official Analytical Chemists
ABSTRACT
Applied and Environmental Microbiology
A procedure is presented for screening the quality of feed in respect to ochratoxin A contaminati... more A procedure is presented for screening the quality of feed in respect to ochratoxin A contamination based upon the analysis of ochratoxin A in pig blood. Representative samples from large feed lots may be obtained by using pigs as in vivo sample collectors which enrich the toxin and forms homogeneous samples in the blood. The spectrofluorometric procedure for ochratoxin A analysis (K. Hult and S. Gatenbeck, J. Assoc. Off. Anal. Chem. 59:128-129, 1976) has been adapted to pig blood and has been simplified to involve only three extraction steps. A volume of 2.5 ml of blood or plasma is needed, and the detection limit is 2 ng of ochratoxin A per ml. The disappearance of ochratoxin A from pig blood as a function of time has been studied. A feeding experiment with ochratoxin A has been performed, and the time course of the concentration of ochratoxin A in blood has been followed during the experiment.