123408-96-8Relevant articles and documents
Stabilisation of transition states prior to and following eudesmane cation in aristolochene synthase
Forcat, Silvia,Allemann, Rudolf K.
, p. 2563 - 2567 (2006)
The mechanistic details of the cyclisation of farnesylpyrophosphate (FPP) by aristolochene synthase (AS) from Penicillium roqueforti have only recently begun to emerge, mainly through the analysis of the reaction products generated by AS-mutants. The reaction proceeds through several intermediates including germacrene A and eudesmane cation. Previous work suggested that the side chain of phenylalanine 178 promoted the conversion of eudesmane cation to aristolochene. We now report that the catalytic function of this residue during the conversion of eudesmane cation to aristolochene is mainly due to the large size of its side chain, which facilitates the hydride shift from C2 to C3, rather than its aromatic character. In addition, F178 appears to control the regioselectivity of the final deprotonation step and, together with F112, helps stabilise the developing positive charge on C1 after the expulsion of pyrophosphate from the substrate. These results complete a screen of likely active-site aromatic residues and establish their respective roles in the conversion of FPP to aristolochene. The Royal Society of Chemistry 2006.
Optimising Terpene Synthesis with Flow Biocatalysis
Tang, Xiaoping,Allemann, Rudolf K.,Wirth, Thomas
, p. 414 - 418 (2017)
Sesquiterpenes are an important family of natural products, many of which exhibit important pharmaceutical and agricultural properties. They are biosynthesised from farnesyl diphosphate in sesquiterpene synthase catalysed reactions. Here, we report the development of a highly efficient segmented flow system for the enzyme-catalysed continuous flow production of sesquiterpenes. Design of experiment (DoE) methods were used to optimise the performance of the flow biocatalysis, and quantitative yields were achieved by using an operationally simple but highly effective segmented flow system.
Accelerating Biphasic Biocatalysis through New Process Windows
Huynh, Florence,Tailby, Matthew,Finniear, Aled,Stephens, Kevin,Allemann, Rudolf K.,Wirth, Thomas
supporting information, p. 16490 - 16495 (2020/07/17)
Process intensification through continuous flow reactions has increased the production rates of fine chemicals and pharmaceuticals. Catalytic reactions are accelerated through an unconventional and unprecedented use of a high-performance liquid/liquid counter current chromatography system. Product generation is significantly faster than in traditional batch reactors or in segmented flow systems, which is exemplified through stereoselective phase-transfer catalyzed reactions. This methodology also enables the intensification of biocatalysis as demonstrated in high yield esterifications and in the sesquiterpene cyclase-catalyzed synthesis of sesquiterpenes from farnesyl diphosphate as high-value natural products with applications in medicine, agriculture and the fragrance industry. Product release in sesquiterpene synthases is rate limiting due to the hydrophobic nature of sesquiterpenes, but a biphasic system exposed to centrifugal forces allows for highly efficient reactions.
Templating effects in aristolochene synthase catalysis: Elimination versus cyclisation
Faraldos, Juan A.,Gonzalez, Veronica,Senske, Michael,Allemann, Rudolf K.
supporting information; experimental part, p. 6920 - 6923 (2011/11/04)
Analysis of the products generated by mutants of aristolochene synthase from P. roqueforti (PR-AS) revealed the prominent structural role played by the aliphatic residue Leu 108 in maintaining the productive conformation of farnesyl diphosphate to ensure C1-C10 (σ-bond) ring-closure and hence (+)-aristolochene production.
Stereochemistry of eudesmane cation formation during catalysis by aristolochene synthase from Penicillium roqueforti
Miller, David J.,Gao, Jiali,Truhlar, Donald G.,Young, Neil J.,Gonzalez, Veronica,Allemann, Rudolf K.
experimental part, p. 2346 - 2354 (2009/02/02)
The aristolochene synthase catalysed cyclisation of farnesyl diphosphate (1) has been postulated to proceed through (S)-germacrene A (3). However, the active site acid that reprotonates this neutral intermediate has so far proved difficult to identify and, based on high level ab initio molecular orbital and density functional theory calculations, a proton transfer mechanism has recently been proposed, in which proton transfer from C12 of germacryl cation to the C6,C7-double bond of germacryl cation (2) proceeds either directly or via a tightly bound water molecule. In this work, the stereochemistry of the elimination and protonation reactions was investigated by the analysis of the reaction products from incubation of 1 and of [12,12,12,13,13,13- 2H6]-farnesyl diphosphate (15) with aristolochene synthase from Penicillium roqueforti (PR-AS) in H2O and D2O. The results reveal proton loss from C12 during the reaction and incorporation of another proton from the solvent. Incubation of 1 with PR-AS in D2O led to the production of (6R)-[6-2H] aristolochene, indicating that protonation occurs from the face of the 10-membered germacrene ring opposite the isopropylidene group. Hence these results firmly exclude proton transfer from C12 to C6 of germacryl cation. We propose here Lys 206 as the general acid/base during PR-AS catalysis. This residue is part of a conserved network of hydrogen bonds, along which protons could be delivered from the solvent to the active site.
Dual role for phenylalanine 178 during catalysis by aristolochene synthase
Forcat, Silvia,Allemann, Rudolf K.
, p. 2094 - 2095 (2007/10/03)
A mutant of aristolochene synthase, in which Phe 178 was replaced by Val, produced significant amounts of α- and β-farnesene as well as α and β-selinene and selina-4,11-diene, suggesting that Phe 178 is involved in the stabilisation of transition states preceding germacrene A and following eudesmane cation.
Aristolochene synthase: Mechanistic analysis of active site residues by site-directed mutagenesis
Felicetti, Brunella,Cane, David E.
, p. 7212 - 7221 (2007/10/03)
Incubation of farnesyl diphosphate (1) with Penicillium roqueforti aristolochene synthase yielded (+)-aristolochene (4), accompanied by minor quantities of the proposed intermediate (S)-(-)germacrene A (2) and the side-product (-)-valencene (5) in a 94:4:2 ratio. By contrast, the closely related aristolochene synthase from Aspergillus terreus cyclized farnesyl diphosphate only to (+)-aristolochene (4). Site-directed mutagenesis of amino acid residues in two highly conserved Mg2+-binding domains led in most cases to reductions in both kcat and kcat/K m as well as increases in the proportion of (S)-(-)germacrene A (2), with the E252Q mutant of the P. roqueforti aristolochene synthase producing only (-)-2. The P. roqueforti D115N, N244L, and S248A/E252D mutants were inactive, as was the A. terreus mutant E227Q. The P. roqueforti mutant Y92F displayed a 100-fold reduction in kcat that was offset by a 50-fold decrease in Km, resulting in a relatively minor 2-fold decrease in catalytic efficiency, kcat/Km. The finding that Y92F produced (+)-aristolochene (4) as 81% of the product, accompanied by 7% 5 and 12% 2, rules out Tyr-92 as the active site Lewis acid that is responsible for protonation of the germacrene A intermediate in the formation of aristolochene (4).
Stabilisation of eudesmane cation by tryptophan 334 during aristolochene synthase catalysis
Deligeorgopoulou, Athina,Taylor, Susan E.,Forcat, Silvia,Allemann, Rudolf K.
, p. 2162 - 2163 (2007/10/03)
Analysis of the hydrocarbons produced during catalysis by mutants of aristolochene synthase from Penicillium roqueforti indicated that Trp 334 had a pivotal function for the efficient production of aristoiochene from farnesylpyrophosphate most likely by stabilising the intermediate, eudesmane cation.
Tyrosine 92 of aristolochene synthase directs cyclisation of farnesyl pyrophosphate
Calvert, Melanie J.,Taylor, Susan E.,Allemann, Rudolf K.
, p. 2384 - 2385 (2007/10/03)
A mutant of Aristolochene Synthase (AS), in which Tyr 92 was replaced by Val, produced the alicyclic β-(E)-farnesene as the major product, indicating that cyclisation of FPP is controlled by Tyr 92 in AS.
Germacrene A is a product of the aristolochene synthase-mediated conversion of farnesylpyrophosphate to aristolochene
Calvert, Melanie J.,Ashton, Peter R.,Allemann, Rudolf K.
, p. 11636 - 11641 (2007/10/03)
The biosynthesis of several sesquiterpenes has been proposed to proceed via germacrene A. However, to date, the production of germacrene A has not been proven directly for any of the sesquiterpene synthases for which it was postulated as an intermediate. We demonstrate here for the first time that significant amounts of germacrene A (7.5% of the total amount of products) are indeed released from wild-type aristolochene synthase (AS) from Penicillium roqueforti. Germacrene A was identified through direct GC-MS comparison to an authentic sample and through production of β-elemene in a thermal Cope rearrangement. AS also produced a small amount of valencene through deprotonation of C6 rather than C8 in the final step of the reaction. On the basis of the X-ray structure of AS, Tyr 92 was postulated to be the active-site acid responsible for protonation of germacrene A (Caruthers, J. M.; Kang, I.; Rynkiewicz, M. J.; Cane, D. E.; Christianson, D. W. J. Biol. Chem. 2000, 275, 25533-25539). The CD spectra of a mutant protein, ASY92F, in which Tyr 92 was replaced by Phe, and of AS were very similar. ASY92F was approximately 0.1% as active as nonmutated recombinant AS. The steady-state kinetic parameters were measured as 0.138 min-1 and 0.189 mM for kcat and KM, respectively. Similar to a mutant protein of 5-epiaristolochene (Rising, K. A.; Starks, C. M.; Noel, J. P.; Chappell, J. J. Am. Chem. Soc. 2000, 122, 1861-1866), the mutant released significant amounts of germacrene A (～29%). ASY92F also produced various amounts of a further five hydrocarbons of molecular weight 204, valencene, β-(E)-farnesene, α- and β-selinene, and selina-4, 11-diene.
