Enzymatic resolution of (±)-cis- and (±)-trans-1-aminoindan-2-ol and (±)-cis- and (±)-trans-2-aminoindan-1-ol

Pseudomonas cepacia lipase (PSL) efficiently catalyses the kinetic resolution of (±)-cis- and (±)-trans-1-aminoindan-2-ol through the O-acylation reaction of the corresponding N-benzyloxycarbonyl derivative using vinyl acetate as the acyl donor. In a similar way, cis-N-Cbz-2-aminoindan-1-ol is resolved when isopropenyl acetate is used as the acylating agent. The enantioselectivity of the reaction was lower for (±)-trans-N-Cbz-2-aminoindan-1-ol due to the different steric requirements for the two conformers of this substrate.     

Facile Resolution of Racemic 4-Phenyl-2-hydroxy Butyrate via Enzymatic Esterification and Transesterification

The optically active R-4-phenyl-2-hydroxy butyrates were prepared by esterification of the racemic acid or transesterification of the racemic ester catalyzed by lipase from Candida cyclindra (CCL) in organic media.     

Gas Chromatographic Determination of Poly(3‐hydroxybutyrate) with Alkaline Hydrolysis and Acid Esterification

Abstract

A new pretreatment method for the gas chromatographic determination of poly(3‐hydroxybutyrate) (PHB) was developed based on a combination of alkaline hydrolysis and acid esterification. The determination principle is as follows: PHB is hydrolyzed to its monomer 3‐hydroxybutyrate by alkaline solution, followed by the esterification with methanol to generate the methyl ester of 3‐hydroxybutyrate catalyzed by acid, which is detected by a gas chromatography. From the comparison of effects of alkali and acid on PHB hydrolysis and 3‐hydroxybutyrate esterification, alkali resulted in a better performance for the hydrolysis, while acid was better for the esterification. The pretreatment conditions for PHB were optimized and the determination performance was characterized.     

Resolution of (±)-2-substituted norbornadiene and hexachloronorbornadiene derivatives using CCL and PLE

(±)-2-Hydroxymethylbicyclo[2.2.1]hepta-2,5-diene, (±)-2-acetoxymethylbicyclo[2.2.1]hepta-2,5-diene and their hexachlorinated derivatives were resolved via CCL- and PLE-catalysed hydrolysis to afford enantiomerically enriched products with e.e.s of 61–93%. The absolute configurations were determined by transforming 2-hydroxymethylbicyclo[2.2.1]hepta-2,5-diene into the 2-formylbicyclo[2.2.1]hepta-2,5-diene with known absolute configuration.     

Facile Syntheses of (±)-Curcuphenol, (±)-Curcudiol, (±)-Curcuhydroquinone,and (±)-Curcuquinone

The syntheses of (±)-curcuphenol 1, (±)-curcudiol 2, (±)-curcuhydroquinone 3, and (±)-curcuquinone 4 have been achieved. The key steps involved in the syntheses were the Reformatsky reaction and hydrogenation reaction.     

Total synthesis of (±)-maistemonine, (±)-stemonamide, and (±)-isomaistemonine

A full account of the total synthesis of (±)-maistemonine, (±)-stemonamide, and (±)-isomaistemonine is presented. Two approaches have been developed to construct the basic pyrrolo[1,2-a]azepine core of the Stemona alkaloids, featuring a tandem semipinacol/Schmidt rearrangement of a secondary azide and a highly stereoselectively desymmetrizing intramolecular Schmidt reaction, respectively. To build the common spiro-γ-butyrolactone, a new protocol was carried out by utilizing an intramolecular ketone-ester condensation as the key transformation. The vicinal butyrolactone moiety of (±)-maistemonine was stereoselectively introduced via a one-pot procedure involving the epimerization at C-3 and carbonyl allylation/lactonization. Moreover, (±)-stemonamide was divergently synthesized from a common intermediate, and (±)-isomaistemonine was obtained via the epimerization of (±)-maistemonine at C-12.     

A new and convenient synthesis of protoberberine alkaloids: (±)-tetrahydropalmatine, (±)-sinactine, (±)-canadine,and (+)-stylopine

2,3,9,10-Tetraoxygenated protoberberine alkaloids (14) were efficiently synthesized from the readily available benzaldehyde (2 or 10) via the benzylphenethylamines (11) and 2-phenethylisoquinolin-3-ones (12 and 13).     

A Convenient Synthesis of 2,4(3H,5H)-Furandione (β-Tetronic Acid)

The chemical versatility of 2,4(3H,5H)-furandione (β-tetronic acid, 1) and its synthetic applicability are of considerable current interest^1b,2a-k. The multifunctional character of this small molecule confers an intriguing synthetic potential which has prompted us to develop synthetic schemes utilizing it as a synthon for certain heterocyclic systems.     

Efficient Synthesis of Biologically Active (±)‐Confluentin and (±)‐Daurichromenic Acid

One‐step synthesis of biologically active (±)‐confluentin is described from commercially available orcinol with trans,trans‐farnesal in the presence of ethylenediamine diacetate as a catalyst. Further conversion of synthetic confluentin to highly potent anti‐HIV agent, (±)‐daurichromenic acid, is accomplished by formylation and oxidation in two steps.     

Total synthesis of (±)-marinopyrrole A via copper-mediated N-arylation

The total synthesis of the racemic form of the marine alkaloid marinopyrrole A is described. The characteristic 1,3'-bipyrrole core was constructed by a copper-mediated N-arylation process under microwave irradiation.     

Optical Resolution ofα-Bromo-2-Chlorophenacetic Acid by Way of Coordination with Copper(II) and O,O’-Dibenzoyltartaric Acid

Optically active molecules play important roles in medicinal chemistry and materials science in both industrial and academic sectors. Resolution is one of the most efficient ways to obtain enantiopure substances. For a long period, racemic carboxylic acids are generally resolved by optically active bases, however, these bases are often extremely toxic and expensive.[1] Recently, A. Mravik Group applied optically active O, O’-dibenzoyltartaric acid (DBTA), which is usually used for the res…     

Hydrolysis Reactions and Resolution of (±)-2-Acetamido-3-hydroxy-1-(4-nitrophenyl)-1-propanone

IntroductionChloramphenicol,which was isolated fromStreptomyces venezuelae in 1 947[1] ,is used as abroad- spectrum antibiotic possessing activityagainst many Gram- negative and Gram- positivemicroorganisms. (± ) - 2 - Acetamido- 3 - hydroxy- 1 -(4- nitrophenyl) - 1 - propanone[(± ) - 1 ]is one of theintermediates of producing chloramphenicol.Petrow et al.[2 ] reported some transformations of(± ) - 1 in hydrolysis reactions. However,thereaction products were complicated under multiplehydr…     

Direct TLC Resolution of (±)-Ketamine and (±)-Lisinopril by Use of (+)-Tartaric Acid or (−)-Mandelic Acid as Impregnating Reagents or Mobile Phase Additives. Isolation of the Enantiomers

Direct resolution of the enantiomers of the racemic drugs ketamine and lisinopril has been achieved by TLC. Enantiomerically pure tartaric acid and mandelic acid were used as chiral impregnating reagents and as mobile phase additives. When (?)-mandelic acid was used as chiral impregnating reagent use of ethyl acetate–methanol–water 3:1:1 (v/v) as mobile phase enabled successful resolution of the enantiomers of both compounds. For lisinopril, the mobile phase acetonitrile–methanol–water–dichloromethane 7:1:1:0.5 (v/v) was successful when (+)-tartaric acid was used as impregnating agent. When (+)-tartaric acid was used as mobile phase additive the mobile phase acetonitrile–methanol–(+)-tartaric acid (0.5% in water, pH 5)–glacial acetic acid 7:1:1.1:0.7 (v/v) enabled successful resolution of the enantiomers of lisinopril. The effects on resolution of temperature, pH, and the amount of chiral selector were also studied. The separated enantiomers were isolated and identified. Spots were detected with iodine vapour. LODs were 0.25 and 0.27 μg for each enantiomer of ketamine with (+)-tartaric acid and (?)-mandelic acid, respectively, whereas for lisinopril LODs were 0.14 and 0.16 μg for each enantiomer with (+)-tartaric acid (both conditions) and (?)-mandelic acid, respectively.     

A direct synthesis of (±)-eldanolide via the highly regioselective prenylation of 2-trimethylsiloxyfuran

The reaction of 2-trimethylsiloxyfuran, 3,3-dimethylallyl bromide and silver trifluoroacetate produced (3,3-dimethylallyl)-4-but-2-en-4-olide with high double regiodifferentiation. The latter compound on treatment with lithium dimethylcuprate gave (±)-eldanolide in high yield.     

Synthesis, Resolution, and Enantiomeric Purity Assay of 2-n-Butylbutanedioic Acid 4-t-Butyl Esters

Introduction2-Substituted enantiomerically pure succinic acidderivatives have attracted a considerable interest in re-cent years,mainly because of their importance as chiralbuilding blocks and peptidomimetics in the field ofpharmaceutical design[1—3].Mos…     

Polymer-Supported Regioselective Synthesis of Methyl 2-O- and 2, 3-Di-O-(4,6-Dimethylpyrimidin-2yl)-α-D-Glucopyranosides

Methyl-α-D-glucopyranoside, stereospecifically protected by polystyrylboronic acid, was then substituted regioselectively by the suitable pyrimidines to yield the novel titled compounds. Various reagents which are able to introduce the pyrimidines onto the polymer-bonded glucoside together with eminent solvent effects on reaction were also studied.     

Straightforward Syntheses of the Three Possible Isomers of (±)-2-[3-(Hydroxybenzoyl) phenyl]propanoic Acid,Metabolites of (±)-Ketoprofen

The o-, m- and p- isomers of (±)-2-[3-(hydroxybenzoyl)phenyl] propanoic acid (11, 12 and 4) have been prepared from 3-bromopropiophenone or m-propionylbenzoic acid, via 7, 8 and 2, which were submitted to Tl(III) nitrateinduced rearrangement, followed by hydrolysis of the ester and ether functions.