Chemoenzymatic Procedure Research Articles

Enzymatic Hydrocyanation of a Sterically Hindered Aldehyde. Optimization of a Chemoenzymatic Procedure for (R)-2-Chloromandelic Acid

The asymmetric synthesis of (R)-o-chloromandelic acid, a key intermediate for the anti-thrombotic agent clopidogrel, via the almond meal catalyzed hydrocyanation of 2-chlorobenzaldehyde and subsequent acidic hydrolysis was developed into an industrially viable procedure. The use of a minimum amount of water consistent with enzyme activity and a slow feed of the reactants were the keys to obtaining (R)-2-chloromandelonitrile in a high (98%) yield and satisfactory (90%) enantiomeric excess. Acidic hydrolysis of the nitrile followed by crystallization from toluene afforded enantiopure (ee > 99%) (R)-2-chloromandelic acid.

Asymmetrized Tris(hydroxymethyl)methane as Precursor of Iminosugars: Application to the Synthesis of Isofagomine.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Asymmetrized tris(hydroxymethyl)methane as precursor of iminosugars: application to the synthesis of isofagomine

A new synthetic application of asymmetrized tris(hydroxymethyl)methane (THYM*), readily obtained in both enantiomeric forms through a chemoenzymatic procedure, is reported. In this case THYM* precursor 3 was elaborated by ring closing metathesis into some enantiopure branched tetrahydropyridines, that have been used as precursors of the potent glycosidase inhibitor isofagomine 28 .

Enantioselective Synthesis of 3-Methylcarbapentofuranose Derivatives, Based on a Chemoenzymatic Procedure

The enantioselective synthesis of 3-methylcarbapentofuranose derivatives through the use of a racemic substituted cyclopentenylcarboxylate as the carbon building block and a number of stereoselective transformations is described. All of the stereogenic centres of these derivatives are directed by the two stereogenic centres created early in the key cyclopentene moiety by a lipase-catalysed enantioselective acetylation. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Chemo-enzymatic synthesis of enantiomerically pure ( R)-2-naphthylmethoxyacetic acid

Enantiomerically pure ( R)-2-naphthylmethoxyacetic acid (2-NMA) was synthesized from 2-naphthaldehyde via an integrated chemo-enzymatic procedure. The one-pot, successive use of SnBr 2–TMSCN and AcBr worked effectively to give a racemic cyanohydrin acetate. Lipase from Burkholderia cepacia then mediated the highly enantioselective hydrolysis of the ( S)-enantiomer of the racemate, leaving the ( R)-acetate with an e.e. of >99.9%. The resulting product of this enzyme-catalyzed hydrolysis, an ( S)-cyanohydrin, spontaneously decomposed into naphthaldehyde, the starting material of this synthetic route, which could be recycled. The hydration of nitrile to amide as well as the hydrolysis of the acetate was performed with a microorganism, Rhodococcus rhodochrous, under very mild conditions without any loss of the enantiomeric purity. The amide group was hydrolyzed with nitrosylsulfuric acid, and the product was isolated as an α-hydroxy ester. The α-hydroxyl group was methylated with diazomethane–silica gel and the final task, hydrolysis of the ester, was accomplished under conditions as mild as neutral pH with an esterase from Krebsiella oxytoca to give enantiomerically pure 2-NMA.

DIFFICULTIES IN THE DEPROTECTION OF 1,2-KETALS IN NUCLEOSIDES CONTAINING ALKYLIDENCARBAZOYL GROUPS

ABSTRACT The synthesis of unprotected alkylidencarbazoyl nucleoside derivatives 8a–8d is shown. A direct deprotection route from readily available 2′,3′-isopropylidene protected nucleosides 5a–5d, prepared from a chemoenzymatic procedure, did not give the selective cleavage of the ketal function without affecting the C˭N bond. The next option tried was to look at the previous compound in the retrosynthetic route: 2′,3′-protected carbazoyl nucleoside 4. However, in all cases we obtained unsatisfactory results. Stepping further back, the hydrolysis of compound 3a led us to unprotected carbonate nucleoside 9 in quantitative yield. With this compound available, the synthesis towards derivatives 8 was accomplished through a known procedure.

Chemo-enzymatic preparation of resveratrol derivatives

Regioselective derivatisation of resveratrol ( 1) at positions 3, 5 or 4′ was achieved by a chemo-enzymatic procedure based on standard chemical reactions and esterification or alcoholysis in organic solvents catalysed by the commercially available Pseudomonas cepacia (PcL) and Candida antarctica (CaL) lipases.

Stereoselective Detoxification of Chiral Sarin and Soman Analogues by Phosphotriesterase

The catalytic activity of the bacterial phosphotriesterase (PTE) toward a series of chiral analogues of the chemical warfare agents sarin and soman was measured. Chemical procedures were developed for the chiral syntheses of the S P- and R P-enantiomers of O-isopropyl p-nitrophenyl methylphosphonate (sarin analogue) in high enantiomeric excess. The R P-enantiomer of the sarin analogue ( k cat=2600 s −1) was the preferred substrate for the wild-type PTE relative to the corresponding S P-enantiomer ( k cat=290 s −1). The observed stereoselectivity was reversed using the PTE mutant, I106A/F132A/H254Y where the k cat values for the R P- and S P-enantiomers were 410 and 4200 s −1, respectively. A chemo-enzymatic procedure was developed for the chiral synthesis of the four stereoisomers of O-pinacolyl p-nitrophenyl methylphosphonate (soman analogue) with high diastereomeric excess. The R P R C-stereoisomer of the soman analogue was the preferred substrate for PTE. The k cat values for the soman analogues were measured as follows: R P R C, 48 s −1; R P S C, 4.8 s −1; S P R C, 0.3 s −1, and S P S C, 0.04 s −1. With the I106A/F132A/H254Y mutant of PTE the stereoselectivity toward the chiral phosphorus center was reversed. With the triple mutant the k cat values for the soman analogues were found to be as follows: R P R C, 0.3 s −1; R P S C, 0.3 s −1; S P R C, 11 s −1, and S P S C, 2.1 s −1. Prior investigations have demonstrated that the S P-enantiomers of sarin and soman are significantly more toxic than the R P-enantiomers. This investigation has demonstrated that mutants of the wild-type PTE can be readily constructed with enhanced catalytic activities toward the most toxic stereoisomers of sarin and soman.

Chemoenzymatic synthesis of 2-chloro-4-nitrophenyl β-maltoheptaoside acceptor-products using glycogen phosphorylase b

In the present work, we aimed at developing a chemoenzymatic procedure for the synthesis of β-maltooligosaccharide glycosides. The primer in the enzymatic reaction was 2-chloro-4-nitrophenyl β-maltoheptaoside (G 7-CNP), synthesised from β-cyclodextrin using a convenient chemical method. CNP-maltooligosaccharides of longer chain length, in the range of DP 8–11, were obtained by a transglycosylation reaction using α- d-glucopyranosyl-phosphate (G-1-P) as a donor. Detailed enzymological studies revealed that the conversion of G 7-CNP catalysed by rabbit skeletal muscle glycogen phosphorylase b (EC 2.4.1.1) could be controlled by acarbose and was highly dependent on the conditions of transglycosylation. More than 90% conversion of G 7-CNP was achieved through a 10:1 donor–acceptor ratio. Tranglycosylation at 37 °C for 30 min with 10 U enzyme resulted in G 8→12-CNP oligomers in the ratio of 22.8, 26.6, 23.2, 16.5, and 6.8%, respectively. The reaction pattern was investigated using an HPLC system. The preparative scale isolation of G 8→11-CNP glycosides was achieved on a semipreparative HPLC column. The productivity of the synthesis was improved by yields up to 70–75%. The structures of the oligomers were confirmed by their chromatographic behaviours and MALDI-TOF MS data.

Asymmetric synthesis of ( R)-(−)-chlozolinate through a chemoenzymatic procedure

A new asymmetric synthesis of ( R)-chlozolinate 1, an important antifungal agent, based on the enzymatic asymmetrization of diethyl 2-benzyloxy-2-methylmalonate, is reported.

Synthesis of novel carbazoyl linked pyrimidine-pyrimidine and pyrimidine-purine dinucleotide analogues

The synthesis of two backbone modified dinucleotide analogues is described in which the natural phosphodiester linkage is replaced by a 3′–5′ carbazoyl linkage. In both cases the bridge was formed through a coupling reaction between an appropriate 3′-carbazoyl nucleoside analogue and an aldehyde nucleoside derivative. It is noteworthy that starting nucleosides 4 could be common materials to obtain the 3′-carbazoyl nucleoside derivatives 2, by means of a simple, previously-described chemoenzymatic procedure, and the aldehyde nucleoside 3, by an oxidation reaction.

Stereoselective Synthesis of 4'-.ALPHA.-Alkylcarbovir Derivatives Based on an Asymmetric Synthesis or Chemoenzymatic Procedure.

Stereoselective synthesis of 4'-α-alkylcarbovir derivatives 4 was described based on asymmetric synthesis or a chemoenzymatic procedure. The asymmetric alkylation of chiral acetal 7 gave the alkylated enol ethers 9a-c possessing a chiral quaternary carbon. The key carbocyclic intermediates 14a-c were synthesized from 9a-c via eleven-steps. Coupling of 14a-c with 2-amino-6-chloropurine followed by desilylation and subsequent hydrolysis afforded the target compounds 4a-c in moderate yield. The optically active cyclopentene intermediates 5a-c and 6a-c were also prepared by enzymatic resolution of (±)-5a-c and (±)-6a-c, respectively.

Chemoenzymatic preparation of 2-chloro-4-nitrophenyl β-maltooligosaccharide glycosides using glycogen phosphorylase b

In the present work, we aimed to develop a new chemoenzymatic procedure for the synthesis of β-maltooligosaccharide glycosides. The primer in the enzymatic reaction was 2-chloro-4-nitrophenyl β-maltoheptaoside (G 7-CNP), which was synthesised from β-cyclodextrin (β-CD) using a very convenient chemical method [E. Farkas, L. Jánossy, J. Harangi, L. Kandra, A. Lipták, Carbohydr. Res., 303 (1997) 407–415]. Shorter chain length CNP-maltooligosaccharides in the range of dp 3–6 were prepared using rabbit skeletal muscle glycogen phosphorylase b (EC 2.4.1.1). Detailed enzymological investigations revealed that the conversion of G 7-CNP was highly dependent on the conditions of phosphorolysis. A 100% conversion of G 7-CNP was achieved during 10 min in 1 M phosphate buffer (pH 6.8) at 30 °C with the tetramer glycoside (77%) as the main product. Phosphorolysis at 10 °C for 10 min resulted in 89% conversion and G 4-, G 5-, and G 6-CNP oligomers were detected in the ratio of 29:26:34%, respectively. The reaction pattern was investigated using an HPLC system. The preparative scale isolation of G 3→6-CNP glycosides was achieved by size-exclusion column chromatography (SEC) on Toyopearl HW-40 matrix. The productivity of the synthesis was improved by yields of up to 70–75%.

Chemoenzymatic Synthesis of Novel 3‘- and 5‘-Carbazoyl Nucleoside Derivatives. Regioselective Preparation of 3‘- and 5‘-Alkylidencarbazoyl Nucleosides

A chemoenzymatic procedure is described for the synthesis of 3‘- and 5‘-carbazoyl nucleoside derivatives 12a,b, 13a,b, 14b,c, and 30b, and these are prepared for the first time. This process involves the regioselective enzymatic alkoxycarbonylation of nucleosides and the subsequent transformation with hydrazine into novel carbazoyl nucleoside derivatives. Taking into account previously reported data (relative to nucleoside, hydrazone, carbazate, and aryloxyphenoxypropionate derivatives), 3‘-alkylidencarbazoyl 2‘-deoxynucleosides 15a,b−18a,b, 5‘-alkylidencarbazoyl 2‘-deoxynucleosides 19a,b−22a,b, 5‘-alkylidencarbazoyl ribonucleosides of uridine 23c−26c, and 5‘-alkylidencarbazoyl-2‘,3‘-isopropylideneadenosine 31b−34b emerge as interesting targets since they combine structural features found in both therapeutic nucleoside derivatives and fungicide/herbicide nucleoside analogues.

Regioselective α(2→3)-Sialylation of LeX and Lea by Sialidase-Catalyzed Transglycosylation1

Considerable effort has been devoted to the development of new methods for α-selective sialylation due to the growing importance of the synthetic sialoglycoconjugates in glycobiology3. The synthesis of α-sialoside has been establised by chemical routes,4 which often involve many steps and are complicated. The promising chemoenzymatic procedure through the use of sialyltransferases has already become a preparative technique.5 However, laborious isolation and the pronounced acceptor specificity of the transferases limit their synthetic potential. Recently, a novel procedure for α-sialylation has been reported, which uses sialosides of synthetic substrate as donors and is catalyzed by sialidase in place of sialyltransferase. Thiem et a1.6 have reported the enzymatic synthesis of α(2→6)-linked sialyl galactose, glucose, lactose and lactosamine in preference to the corresponding α(2→3)-linked derivatives employing sialidase from vibrio cholerae, while Ajisaka et al.7 have synthesized α(2→3)-linked sialyl lactose and lactosamine with sialidase from new castle disease virus. 1. Synthetic studies on sialoglycoconjugates, Part 101. For Part 100, see H. Ito, H. Ishida, M. Kiso and A. Hasegawa, Carbohydr. Res., 306, 1 (1998).

Chemoenzymatic Synthesis of Optically Pure Planar Chiral (S)-(–)-5-Formyl-4-hydroxy[2.2]paracyclophane

The synthesis of optically pure (S)-5-formyl-4-hydroxy-[2.2]paracyclophane (S)-3 (ee > 99 %) was achieved by a three-step chemoenzymatic procedure consisting of (i) kinetic enzymatic resolution of (R, S)-4-acetoxy[2.2]para-cyclophane (R, S)-1 to produce optically pure starting material, which after (ii) hydrolysis was subjected to (iii) stereoselective ortho-formylation with an overall yield of 51 %. All attempts to use a biocatalyst directly for the preparation of optically pure disubstituted [2.2]para-cyclophanes failed because of either total lack of activity (bioreduction) or low enantioselectivities of the enzymes screened (hydrolases). Using the chemoenzymatic approach from (R, S)- 1, optically pure (S)-1 and after subjecting (S)-1 to hydrolysis and finally to formylation (S)-3 was obtained. As confirmed by chiral GC, hydrolysis and formylation took place without racemization. During the optimization of the enzymatical part of the synthesis a strong influence of both the nature of the cosolvent and the pH of the buffer-phase on the enantioselectivity value E were observed. Using a two-phase system consisting of diethyl ether and phosphate buffer an E value higher than 100 was achieved at a pH of 7.0 and at room temperature.

Highly swelling hydrogels from ordered galactose-based polyacrylates

High swelling galactose-based hydrogels have been prepared using a chemoenzymatic procedure. Regioselective acylation of β-O-methyl-galactopyranoside in nearly anhydrous pyridine with lipase from Pseudomonas cepacia yields the 6-acryloyl derivative (Compound I). Further lipase-catalysed acylation of the monoacrylate derivative in nearly anhydrous acetone yielded 2,6-diacryloyl- β-O-methyl galactopyranoside (Compound II) that can act as a cross-linker with a structure similar to that of the sugar-based monomer. The high selectivity of enzyme catalysis yielded apparently highly regular hydrogel networks with swelling ratios at equilibrium ranging from 170 to 1100, elastic moduli ranging from 0.005 to 0.088 MPa and calculated mesh sizes ranging from 1160 to 6600 Å. These values are far higher than conventional uncharged or lightly charged hydrogels at similar elastic moduli. Gel swelling was fast, with 75% of the equilibrium swelling value reached in a fractional time of 0.17. Non-selective chemical acryloylation of β-O-methyl galactopyranoside followed by polymerization yielded a far lower-swelling hydrogel than that obtained using selective enzyme catalysis. These results indicate that the highly regular polymer structure achieved by regioselective enzyme-catalysed acylation yields relatively strong and highly swellable materials. Sugar-based hydrogels, such as those described herein, may find particular use as biomaterials because of their high water content, homogeneity, stability and expected non-toxicity. A wide range of pore sizes can be attained, suggesting that they may also be especially useful as matrices for enzyme immobilization and controlled delivery of biological macromolecules.

Synthetic methods of glycopeptide assembly, and biological analysis of glycopeptide products

The technology of glycopeptide synthesis has recently developed into a fully mature science capable of creating diverse glycopeptides of biological interest, even in combinatorial displays. This has allowed biochemists to investigate substrate specificity in the biosynthetic processing and immunology of various protein glycoforms. The construction of all the mucin core structures and a varietyof cancer-related glycopeptides has facilitated detailed analysis of the interaction between MHC-bound glycopeptides and T cell receptors. Novel dendritic neoglycopeptide ligands have been shown to demonstrate high affinity for carbohydrate receptors and these interactions are highly dendrimer specific. Large complex N-linked oligosaccharides have been introduced into glycopeptides using synthetic or chemoenzymatic procedures, both methods affording pure glycopeptides corresponding to a single glycoform in preparative quantities. The improved availability of glycosyl transferases has led to increased use of chemoenzymatic synthesis. Chemical ligation has been introduced as a method of attaching glycans to peptide templates. Combinatorial synthesis and the analysis of resin-bound glycopeptide libraries have been successfully carried out by applying the ladder synthesis principle. Direct quantitative glycosylation of peptide templates on solid phase has paved the way for the synthesis of templated glycopeptide mixtures as libraries of libraries.

Application of (2 R,3 R)-dihydroxy-1,2,3,4-tetrahydronaphthalene to asymmetric synthesis

(2 R,3 R)-Dihydroxy-tetrahydronaphthalene, prepared via an efficient chemoen-zymatic procedure from naphthalene, has been successfully tested, as a chiral auxiliary in diastereoselective conjugate additions of lithium dialkylcuprates to α,β-unsaturated esters and in stereoselective alkylations of β-ketoesters.

ChemInform Abstract: Enantio‐ and Diastereoselective Synthesis of the AB Ring System of Aklavinone by Coupling a Chemoenzymatic Procedure with Organometal Chemistry.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.