Enzyme-catalyzed synthesis of furanosyl nucleotides

A bacterial alpha-d-glucopyranosyl-1-phosphate thymidylyltransferase was found to couple four hexofuranosyl-1-phosphates, as well as a pentofuranosyl-1-phosphate, with deoxythymidine 5'-triphosphate, providing access to furanosyl nucleotides. The enzymatic reaction mixtures were analyzed by electrospray ionization mass spectrometry and NMR spectroscopy to determine the anomeric stereochemistry of furanosyl nucleotide products. This is the first demonstration of a nucleotidylyltransferase discriminating between diastereomeric mixtures of sugar-1-phosphates to produce stereopure, biologically relevant furanosyl nucleotides.     

Enzyme-catalyzed synthesis of natural and unnatural polysaccharides

Synthesis of natural and unnatural polysaccharide was achieved via “enzymatic polymerization” by utilizing a glycoside hydrolase as catalyst. Particularly, hyaluronan, chondroitin, and their derivatives belonging to glycosaminoglycans have been prepared using sugar oxazoline monomers designed on the basis of the concept “transition-state analogue substrate”. The oxazoline derivatives of N-acetylhyalobiuronate [GlcAβ(1→3)GlcNAc] and N-acetylchondrosine [GlcAβ(1→3)GalNAc], which have the repeating disaccharide structures of hyaluronan and chondroitin, respectively, were successfully polymerized by the catalysis of hyaluronidase, giving rise to synthetic hyaluronan and chondroitin. Their 2-substituted oxazoline derivatives were also polymerized to the corresponding N-acylated hyaluronan and chondroitin derivatives. Furthermore, N-acetylchondrosine oxazoline derivatives sulfated at the C4, the C6, and both the C4 and C6 of the GalNAc unit were catalyzed by hyaluronidase; the monomer sulfated at the C4 was polymerized to chondroitin 4-sulfate with well-defined structure, whereas the other two monomers were exclusively hydrolyzed to the corresponding disaccharides. These different kinds of natural and unnatural polysaccharides having relatively high molecular weights were produced in all cases by the catalysis of hyaluronidase. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5014–5027, 2006     

Enzyme-catalyzed peptide synthesis in biphasic aqueous-organic systems

A preparative protease-catalyzed peptide synthesis in biphasic aqueous-organic systems is described. This approach using both free as well as immobilized proteases as catalysts provides high yields and includes the possibility to re-utilize the enzymes.     

Enzyme-catalyzed synthesis of nucleoside triphosphates from nucleoside monophosphates

Syntheses of adenosine 5′-triphosphate (ATP) from adenosine 5′-monophosphate (AMP) and ribavirin 5′-triphosphate (RTP) from ribavirin 5′-monophosphate (RMP) (1) were performed using enzymes as catalysts. Synthesis of ATP is based on acetyl phosphate as the phosphate donor, and acetate kinase (Bacillus stearothermophilus, EC 2.7.2.1), adenylate kinase (porcine muscle, EC 2.7.4.3), and inorganic pyrophosphatase (yeast, EC 2.6.1.1) as the catalysts. Three reactions on a 150-mmol scale provided ATP as its barium salt in 82% yield and 67% purity. Synthesis of RTP used phosphoenol pyruvate (PEP) as the phosphate donor, and pyruvate kinase (rabbit muscle, EC 2.7.1.40) and adenylate kinase (rabbit muscle) as the catalysts. A gram-scale reaction provided RTP as its barium salt in 93% yield and 97% purity. This work demonstrates the utility of the autoxidationresistant acetate kinase fromB. stearothermophilus, the value of pyrophosphatase in controlling the level of pyrophosphate in the reactions and the ability of adenylate kinase to accept at least one substrate other than a derivative of adenosine.     

Enzyme-catalyzed synthesis of a novel thermosensitive polyester with pendant ketoprofen

A novel thermosensitive polyester with pendant ketoprofen was synthesized by copolymerization of PEG 800 with 2‐ketoprofendimethylmalate using CAL‐B at 70 °C. The products were characterized by NMR spectra and GPC. The in vitro study demonstrated that the polyester could release ketoprofen in physiological conditions, which indicates that the polyester could be a promising prodrug.

     

Three-component diastereoselective cascade synthesis of thiohydantoins

A new three-component cascade reaction for the synthesis of thiohydantoins is reported. The reaction between α-amino esters, nitrostyrenes, and aromatic isothiocyanates is efficiently promoted by organic bases to afford highly substituted thiohydantoins in moderate to good yields and diastereoselectivities.     

Highly enantioselective cascade synthesis of spiropyrazolones

An efficient synthesis of spiropyrazolones based on organocatalysis is described. The reaction between pyrazolones, enolizable aldehydes and enals is catalyzed by secondary amine catalysts and affords the final spiro compounds bearing four contiguous chiral centers in good yields and excellent diastereo- and enantioselectivities.     

Enzyme-catalyzed organic synthesis of sucrose and trehalose with in situ regeneration of UDP-Glucose

This paper describes cell-free enzymatic syntheses of sucrose and trehalose using partially-purified preparations of sucrose and trehalose synthetase. The coupling of the regeneration of uridine-5′-diphosphoglucose (UDP-Glc) with synthesis of the disaccharide offers a practical route to millimol quantities of these carbohydrates. The syntheses used pyruvate kinase, UDP-Glc pyrophosphorylase, and inorganic pyrophosphatase, and the regenerated UDP-Glc was cycled approximately 10 times. This work was supported by the NIH through several grants, most recently GM 30367.     

One-pot synthesis of furocoumarins through cascade addition-cyclization-oxidation

A novel one-pot cascade addition-cyclization-oxidation for the regioselective synthesis of furo[3,2-c]coumarins has been developed; the reaction is mild and easily handled without the necessity for dry solvents and inert atmosphere.     

酶催化聚合研究进展

酶催化聚合是最近发展起来的一种新型聚合方法，能在温和的条件下，高效率、高选择性地完成聚合反应，将对未来工业聚合方法产生深远影响。较详细地综述了近年来酶催化聚合，特别是缩聚反应和开环聚合的研究进展。     

Enzyme-catalyzed,gas-phase reactions

UV-49, the mutant ofPenicillium funiculosum, showed higher production of cellulase although the specific activity with regards to filter paper activity was unaltered (0.7 U/mg). Fractionation of culture filtrates by isoelectric focusing indicated the presence of three endoglucanases and two β-glucosidases in the parent strain, whereas one endoglucanase and one β-glucosidase for UV-49. The thermostability of activity towards filter paper, CM-cellulose and ρ-nitrophenyl-β-D-glucoside of the parent strain was about 30–50% more than the corresponding activities of the mutant. The saccharification of bagasse with the enzymes from parent (66%) and mutant (62%) was comparable. However, the recovery of enzyme from residual cellulose was 10–20% less in case of the mutant. The formation of higher oligosaccharides in the hydrolysates of UV-49 on prolonged incubation indicated the presence of transglycosylation activity in the enzyme complex. In contrast the parent strain produces glucose; the desired end product of the practical saccharification.     

One-pot catalytic asymmetric cascade synthesis of cycloheptane derivatives

A regiospecific, highly chemo-, diastereo-, and enantioselective one-pot catalytic cascade synthesis of cycloheptane derivatives is presented. In this chiral-amine-catalyzed asymmetric process, six new bonds and five new stereocenters were formed with excellent stereocontrol (>25:1 d.r. and 98- >99 ee).     

Enzymatic polyesterification in organic media. II. Enzyme-catalyzed synthesis of lateral-substituted aliphatic polyesters and copolyesters

Enzymatic polymerization of hydroxyesters in organic media has been the subject of a previous and ongoing research in our laboratory. As part of that study, four ?-substituted-?-hydroxyesters were synthesized, and then polymerized using crude porcine pancreatic lipase (PPL) in n-hexane. These lateral-substituted hydroxyesters polymerized enantioselectively to produce optically active oligomers and a resolved optically active unreacted monomer. It was found that with increasing bulkiness of the lateral substituent, in the order Me >Et >Ph, the enzymatic reaction becomes slower, yet the enantioselectivity is higher. The lateral-substituted hydroxyesters were also copolymerized enzymatically with the more reactive linear methyl ?-hydroxyhexanoate. Optically active copolymers were obtained, higher in molecular weight than the analogous homopolymers. © 1993 John Wiley & Sons, Inc.     

Enzyme-catalyzed enantioselective diaryl ketone reductions

The synthesis of diarylmethanols via the reduction of a range of substituted benzophenone and benzoylpyridine derivatives with ketoreductase enzymes (KREDs) has afforded chiral products with high yield (>90%) and ee (up to >99%). Ortho, meta, and para substitutions with a variety of electron-donating, electron-withdrawing, and halogen groups were examined. Substitution at the ortho position and/or highly electronically dissymmetric molecules were not required for good selectivity, as is the case with conventional chemical catalyst reductions. [reaction: see text].     

Enzyme-catalyzed regioselective transesterification of peracylated sophorolipids

Regioselective transesterifications and hydrolysis of peracylated sophorolipid (SL) derivatives catalyzed by lipases was investigated. This study is the first evaluation of the lipase-catalyzed reactions on the non-lactonic SL derivatives. Four lipases, namely from porcine pancreas (PPL, Type II), Candida rugosa (AYS, TypeVII), Pseudomonas cepacia (PS-30), and Candida antarctica (Novozym 435, carrier fixed lipase fraction B) were used in anhydrous THF or in phosphate buffer (pH=7.4, 0.2 M). It was confirmed from the detailed spectral analysis of the products that transesterification failed to furnish any free hydroxyls on the sophorose ring. Instead, transesterification took place on the methyl ester located at the carboxylic end of the 17-hydroxyoctadecenoic acid chain attached to the C-1′ position of the sophorose ring. It is proposed that in absence of the lactonic structural motif, the binding of the peracylated non-lactonic SLs in the lipase binding pocket takes place such that the carboxyl group of the octadecenoic acid, not the sophorose sugar, is preferentially accessible to the active site.     

酶促Michael-aldol串联反应合成四氢噻吩类化合物

在水介质和40℃条件下,碱性蛋白酶催化2,5-二羟基-1,4-二噻烷与N-苯基马来酰亚胺间的Michael-aldol反应,合成了四氢噻吩类化合物,反应取得了93%的产率及3∶1的非对映选择性。该方法具有反应条件温和、反应时间短、后处理简单等优点。     

Efficient synthesis of furoquinolinones using Hendrickson reagent-initiated cascade annulation

A new synthesis of furo[3,4-b]quinolin-3(1H)-one derivatives has been established in straightforward fashion in high overall yields. An efficient Hendrickson reagent-initiated cascade annulation, which is composed of mild conversion of the stable amide precursor to the reactive imido-carbonium intermediate and subsequent intramolecular aza Diels-Alder reaction, successfully serves as the key reaction in the synthesis. Final oxidative cleavage of the carbon-carbon double bond of representative tricyclic precursor 8g led to completion of the synthesis of quinoline-lactone 2g in a high yield.     

A denitrogenative palladium-catalyzed cascade for regioselective synthesis of fluorenes

We herein report a denitrogenative palladium-catalyzed cascade for the modular and regioselective synthesis of polysubstituted fluorenes. Hydrazone facilitates the Pd(ii) to Pd(iv) oxidative addition in a Catellani pathway and is also the methylene synthon in the proposed reaction. Aryl iodides and 2-bromoarylaldehyde hydrazones undergo a norbornene-controlled tandem reaction sequence to give a broad scope of fluorenes in the presence of a palladium catalyst. The method described is scalable and adaptable to a three-component reaction with in situ generation of the hydrazone group. Preliminary mechanistic investigations have been conducted.

Hydrazone assists Pd(ii)/(iv) oxidative addition and is the methylene synthon in a palladium-catalyzed, norbornene-mediated regioselective synthesis of fluorenes.