Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Mechanistic insights into the cytochrome P450-mediated oxidation and rearrangement of littorine in tropane alkaloid biosynthesis
AU - Nasomjai, Pitak
AU - Reed, Darwin W.
AU - Tozer, David J.
AU - Peach, Michael J. G.
AU - Slawin, Alexandra M. Z.
AU - Covello, Patrick S.
AU - O'Hagan, David
PY - 2009/9/21
Y1 - 2009/9/21
N2 - During the biosynthesis of certain tropane alkaloids, littorine (1) is rearranged to hyoscyamine (3). Recent evidence indicates that this isomerisation is a two-step process in which the first step is an oxidation/rearrangement to give hyoscyamine aldehyde (2). This step is catalysed by CYP80F1, a cytochrome P450 enzyme, which was recently identified from the plant Hyoscyamus niger; CYP80F1 also catalyses the hydroxylation of littorine at the 3'-position. The mechanisms of the reactions catalysed by CYP80F1 were probed with synthetic deutero and arylfluoro analogues of 1. Measurement of the primary kinetic isotope effects indicates that C3' hydrogen abstraction is the rate-limiting step for the oxidation/rearrangement of natural littorine, and for the 3'-hydroxylation reaction of the unnatural S enantiomer of littorine. The character of the intermediates in the oxidation/rearrangement and hydroxylation reaction was probed with the use of arylfluorinated analogues of (R)-littorine (natural stereoisomer) and (S)-littorine (unnatural stereoisomer) as substrates for CYP80F1. The relative conversions of ortho-, meta- and para-fluorolittorine analogues were used to obtain information on the likely intermediacy of either a benzylic radical or benzylic carbocation intermediate. The data suggest that hydroxylation takes place via a benzylic carbocation intermediate, whereas the product profile arising from rearrangement is more consistent with a benzylic radical intermediate.
AB - During the biosynthesis of certain tropane alkaloids, littorine (1) is rearranged to hyoscyamine (3). Recent evidence indicates that this isomerisation is a two-step process in which the first step is an oxidation/rearrangement to give hyoscyamine aldehyde (2). This step is catalysed by CYP80F1, a cytochrome P450 enzyme, which was recently identified from the plant Hyoscyamus niger; CYP80F1 also catalyses the hydroxylation of littorine at the 3'-position. The mechanisms of the reactions catalysed by CYP80F1 were probed with synthetic deutero and arylfluoro analogues of 1. Measurement of the primary kinetic isotope effects indicates that C3' hydrogen abstraction is the rate-limiting step for the oxidation/rearrangement of natural littorine, and for the 3'-hydroxylation reaction of the unnatural S enantiomer of littorine. The character of the intermediates in the oxidation/rearrangement and hydroxylation reaction was probed with the use of arylfluorinated analogues of (R)-littorine (natural stereoisomer) and (S)-littorine (unnatural stereoisomer) as substrates for CYP80F1. The relative conversions of ortho-, meta- and para-fluorolittorine analogues were used to obtain information on the likely intermediacy of either a benzylic radical or benzylic carbocation intermediate. The data suggest that hydroxylation takes place via a benzylic carbocation intermediate, whereas the product profile arising from rearrangement is more consistent with a benzylic radical intermediate.
KW - DATURA-STRAMONIUM
KW - STEREOCHEMICAL COURSE
KW - isomerization
KW - alkaloids
KW - P450-CATALYZED HYDROXYLATION
KW - SUBSTITUTION
KW - CARBON-SKELETON REARRANGEMENT
KW - TROPIC ACID
KW - cytochromes
KW - PROBES
KW - enzyme catalysis
KW - ENZYME
KW - fluorine
KW - HYOSCYAMINE
KW - REACTIVITY
U2 - 10.1002/cbic.200900318
DO - 10.1002/cbic.200900318
M3 - Journal article
VL - 10
SP - 2382
EP - 2393
JO - ChemBioChem
JF - ChemBioChem
SN - 1439-4227
IS - 14
ER -