Racemic Ethyl Research Articles

Protein engineering of an alkaline protease from Bacillus licheniformis (BLAP) for efficient and specific chiral resolution of the racemic ethyl tetrahydrofuroate

Enzymatic resolution of ethyl tetrahydrofuroate to produce (S)-2-ethyl tetrahydrofuroate and (R)-2-tetrahydrofuroic acid is a green biomanufacturing strategy. However, enzymatic activity and selectivity are still limiting factors of their industrial applications and development. In previous study, we incidentally found that a Bacillus licheniformis alkaline protease (BLAP), not a lipase, could specifically resolve ethyl tetrahydrofuroate to produce (S)-2-ethyl tetrahydrofuroate and (R)-2-tetrahydrofuroic acid. In this study, the point-saturation-mutation libraries based on the seven amino acid sites (L105, I113, P114, L115, V309, Y310, and M326) were constructed and screened using the molecular docking technology. It was found that activity of the mutant BLAPY310E reached 182.78 U/mL with high stereoselectivity, 3.14 times higher than that of the wild-type BLAP. Further simulated mutation analysis showed that the Y310E mutation increased the distance from the substrate ligand to the binding pocket from 2.3 Å to 4.5 Å, reducing steric hindrance to the active center. Under the optimal conditions and after 3.5 h of reaction catalyzed by BLAPY310E, 200 mM ethyl tetrahydrofuroate was converted to (S)-2-ethyl tetrahydrofuroate and (R)-2-tetrahydrofuroic acid with the ee values of 99.9 % and 68.63 %, respectively. The enantiomeric ratio of BLAPY310E was 105.5, which was 30.23 times higher than that of BLAP. This study advances the comprehension of protease activity and selectivity mechanisms in resolving ester substances and lays a robust foundation for the industrial production of the optically pure (S)-2-ethyl tetrahydrofuroate and (R)-2-tetrahydrofuroic acid via biological enzymatic methods.

Chemical Synthesis of Atactic Poly-3-hydroxybutyrate (a-P3HB) by Self-Polycondensation: Catalyst Screening and Characterization.

Poly-3-hydroxybutyrate (P3HB) is a biodegradable polyester produced mainly by bacterial fermentation in an isotactic configuration. Its high crystallinity (about 70%) and brittle behavior have limited the process window and the application of this polymer in different sectors. Atactic poly-3-hydroxybutyrate (a-P3HB) is an amorphous polymer that can be synthesized chemically and blended with the isotactic P3HB to reduce its crystallinity and improve its processability Ring-opening polymerization (ROP) is the most cited synthesis route for this polymer in the literature. In this work, a new synthesis route of a-P3HB by self-polycondensation of racemic ethyl 3-hydroxybutyrate will be demonstrated. Different catalysts were tested regarding their effectiveness, and the reaction parameters were optimized using titanium isopropoxide as the catalyst. The resulting polymers were compared by self-polycondensation for their properties with those of a-P3HB obtained by the ROP and characterized by Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC), and the double bond content (DBC) was determined by UV-VIS spectroscopy by using 3-butenoic acid as a standard. Additionally, a life cycle analysis (LCA) of the new method of synthesizing has been carried out to assess the environmental impact of a-P3HB.

Chemoenzymatic Stereodivergent Synthesis of All the Possible Stereoisomers of the 2,3-Dimethylglyceric Acid Ethyl Ester

2,3-dihydroxy-2-methylbutyric acid, also known as 2,3-dimethylglyceric acid, constitutes the acyl and/or the alcoholic moiety of many bioactive natural esters. Herein, we describe a chemoenzymatic methodology which gives access to all the four possible stereoisomers of the 2,3-dimethylglyceric acid ethyl ester. The racemic ethyl α-acetolactate, produced by the N-heterocycle carbene (NHC)-catalyzed coupling of ethyl pyruvate and methylacetoin was employed as the starting material. The racemic mixture was resolved through (S)-selective reductions, promoted by the acetylacetoin reductase (AAR) affording the resulting ethyl (2R,3S)-2,3-dimethylglycerate; the isolated remaining (S)-ethyl α-acetolactate was successively treated with baker’s yeast to obtain the corresponding (2S,3S) stereoisomer. syn-2,3-Dimethylgliceric acid ethyl ester afforded by reducing the rac-α-acetolactate with NaBH4 in the presence of ZnCl2 was kinetically resolved through selective acetylation with lipase B from Candida antarctica (CAL-B) and vinyl acetate to access to (2S,3R) stereoisomer. Finally, the (2R,3R) stereoisomer, was prepared by C3 epimerization of the (2R,3S) stereoisomer recovered from the above kinetic resolution, achieved through the TEMPO-mediated oxidation, followed by the reduction of the produced ketone with NaBH4. The resulting 2,3-dimethylglycertate enriched in the (2R,3R) stereoisomer was submitted to stereospecicific acetylation with vinyl acetate and CAL-B in order to separate the major stereoisomer. The entire procedure enabled conversion of the racemic α-acetolactate into the four enantiopure stereoisomers of the ethyl 2,3-dihydroxy-2-methylbutyrate with the following overall yields: 42% for the (2R,3S), 40% for the (2S,3S), 42% for the (2S,3R) and 20% for the (2R,3R).

Enhanced Production of (S)-2-arylpropionic Acids by Protein Engineering and Whole-Cell Catalysis.

Esterases are important biocatalysts for chemical synthesis. Several bHSL family esterases have been used to prepare (S)-2-arylpropionic acids with stronger anti-inflammatory effects via kinetic resolution. Here, we presented the discovery of key residues that controlled the enantioselectivity of bHSL family esterases to ethyl 2-arylpropionates, through careful analysis of the structural information and molecular docking. A new bHSL family esterase, Est924, was identified as a promising catalyst for kinetic resolution of racemic ethyl 2-arylpropionates with slight (R)-stereopreference. Using Est924 as the starting enzyme, protein engineering was conducted at hotspots, and the substitution of A203 was proved to enhance the enantioselectivity. The stereopreference of the mutant M1 (A203W) was inverted to ethyl (S)-2-arylpropionates, and this stereopreference was further improved in variant M3 (I202F/A203W/G208F). In addition, the optimal variant, M3, was also suitable for the resolution of ibuprofen ethyl ester and ketoprofen ethyl ester, and their efficient (S)-isomers were synthesized. Next, the whole-cell catalyst harboring M3 was used to prepare (S)-ketoprofen. (S)-ketoprofen with 86%ee was produced by whole-cell catalyst with a single freeze-thaw cycle, and the cells could be reused for at least five cycles. Our results suggested that Est924 variants could kinetically resolve economically important racemates for industrial production and further offer the opportunity for the rational design of enzyme enantioselectivity. Moreover, it is an economical process to prepare optically pure (S)-ketoprofen and (S)-naproxen by using an engineered strain harboring M3 as the catalyst.

Multigram‐scale HPLC enantioseparation as a rescue pathway for circumventing racemization problem during enantioselective synthesis of ethyl 3,4‐dihydro‐2H‐1,4‐benzoxazine‐2‐carboxylate

Racemic ethyl 3,4-dihydro-2H-1,4-benzoxazine-2-carboxylate is a key synthon for the design of promising therapeutic drugs. It is mainly synthesized from racemic ethyl 2,3-dibromopropionate and 2-aminophenol in presence of K2 CO3 in refluxed acetone. Unfortunately, synthesis of (R)- and (S)-enantiomers using the enantioselective version of this reaction, which should normally be performed with a double SN 2 mechanism, is unsuitable due to a racemization process involving the dehydrobromination of enantiopure ethyl 2,3-dibromopropionate into ethyl 2-bromoacrylate. For the first time, the enantioselective version is studied (ee ≈ 55-66%), and the percentage of racemization process has estimated to around 34-46% after determination of the optimal experimental conditions for analytical HPLC enantioseparation of racemate. The influence of the experimental and purification conditions on the racemization rate is also studied. The results indicate that racemization occurs faster at the beginning of the reaction but the initiation of the double SN 2 process takes place more faster to limit the racemization rate. The study of the influence of experimental conditions (reaction times, temperature, solvent or type of base, etc.) on the degree of racemization of the (R)- enantiomer is performed and shows that despite changes in the experimental conditions, the synthesis of the (R)- enantiomer is always accompanied by a racemization rate which is difficult in reducing. In parallel, (R)- and (S)-enantiomers are obtained in high enantiopurity (ee > 99.5%) by preparative HPLC enantioseparation of racemate on multigram scale and characterized by optical rotation measurements, ECD and UV spectra.

An Alternative Enzymatic Route to the Ergogenic Ketone Body Ester (R)-3-Hydroxybutyl (R)-3-Hydroxybutyrate

Recent studies have highlighted the therapeutic and ergogenic potential of the ketone body ester, (R)-3-hydroxybutyl-(R)-3-hydroxybutyrate. In the present work, the enzymatic synthesis of this biological active compound is reported. The (R)-3-hydroxybutyl-(R)-3-hydroxybutyrate has been produced through the transesterification of racemic ethyl 3-hydroxybutyrate with (R)-1,3-butanediol by exploiting the selectivity of Candida antarctica lipase B (CAL-B). The needed (R)-1,3-butanediol was in turn obtained from the kinetic resolution of the racemate achieved by acetylation with vinyl acetate, also in this case, thanks to the enantioselectivity of the CAL-B used as catalyst. Finally, the stereochemical inversion of the unreacted (S) enantiomers of the ethyl 3-hydroxybutyate and 1,3-butanediol accomplished by known procedure allowed to increase the overall yield of the synthetic pathway by incorporating up to 70% of the starting racemic reagents into the final product.

Enantiopure ethyl 2,3-dibromopropionate: Enantioselective synthesis vs preparative HPLC enantioseparation of racemate on multigram scale.

Racemic ethyl 2,3-dibromopropionate, commercially available at low price, is a key intermediate used in the synthesis of several heterocycle fragments, which are present in many biologically active compounds. Surprisingly, the enantiomers are not commercially available and have never been described in the literature. In this work, we undertook two different strategies to obtain these enantiomers, which are enantioselective synthesis and preparative HPLC enantioseparation of commercially available racemate on multigram scale. The first strategy has proved inadequate because racemization occurred during the synthesis (ee ≈ 9-50%). Conversely, the second strategy produced a very good enantioseparation of commercially available racemate (ee > 99.5% for both enantiomers) on multigram scale.

Functional Characterization of a Robust Marine Microbial Esterase and Its Utilization in the Stereo-Selective Preparation of Ethyl (S)-3-Hydroxybutyrate.

One novel microbial esterase PHE21 was cloned from the genome of Pseudomonas oryzihabitans HUP022 identified from the deep sea of the Western Pacific. PHE21 was heterologously expressed and functionally characterized to be a robust esterase which behaved high resistance to various metal ions, organic solvents, surfactants, and NaCl. Despite the fact that the two enantiomers of ethyl 3-hydroxybutyrate were hard to be enzymatically resolved before, we successfully resolved racemic ethyl 3-hydroxybutyrate through direct hydrolysis reactions and generated chiral ethyl (S)-3-hydroxybutyrate using esterase PHE21. After process optimization, the enantiomeric excess, the conversion rate, and the yield of desired product ethyl (S)-3-hydroxybutyrate could reach 99, 65, and 87%, respectively. PHE21 is a novel marine microbial esterase with great potential in asymmetric synthesis as well as in other industries.

Purification and Immobilization of a Novel Enantioselective Lipase from Tsukamurella tyrosinosolvents for Efficient Resolution of Ethyl 2-(2-oxopyrrolidin-1-yl) Butyrate.

A highly enantioselective lipase from Tsukamurella tyrosinosolvents E105 was purified via ultrasonic extraction, precipitation, and chromatographic steps. The enzyme was purified about 38-fold with the recovery yield of 9% and was confirmed as a dimer protein consisting of two identical subunits with a molecular mass of 24kDa. The purified lipase was used to catalyze resolution of racemic ethyl 2-(2-oxopyrrolidin-1-yl) butyrate to (S)-2-(2-oxopyrrolidin-1-yl) butyric acid. The maximum activity of such lipase was obtained at pH7.5, 35°C, and the highest relative activity (156.80%) was observed in the presence of 0.5mM Co2+. Subsequently, the lipase was encapsulated within a mixture of 3% sodium alginate and 0.8% carrageenan, and then cross-linked with 0.6% glutaraldehyde to enhance its biocatalytic capability and stability. Comparing with 36.9% product yield and 97.5% product ee of free lipase, the highest product yield of 46.3% and ee of 98.5% for immobilized lipase were achieved with the presence of 20mM substrate. In addition, the reusability of immobilized lipase was also investigated, which could maintain 63.7% of its initial conversion yield after seven repeated batch reactions. Thus, the evaluated enantioselective lipase in this work has a good potential for further industrial application.

Bioresolution production of (2R,3S)-ethyl-3-phenylglycidate for chemoenzymatic synthesis of the taxol C-13 side chain by Galactomyces geotrichum ZJUTZQ200, a new epoxide-hydrolase-producing strain.

A newly isolated Galactomyces geotrichum ZJUTZQ200 strain containing an epoxide hydrolase was used to resolve racemic ethyl 3-phenylglycidate (rac-EPG) for producing (2R,3S)-ethyl-3-phenylglycidate ((2R,3S)-EPG). G. geotrichum ZJUTZQ200 was verified to be able to afford high enantioselectivity in whole cell catalyzed synthesis of this chiral phenylglycidate synthon. After the optimization of the enzymatic production and bioresolution conditions, (2R,3S)-EPG was afforded with high enantioselectivity (e.e.S > 99%, E > 49) after a 8 h reaction. The co-solvents, pH buffer solutions and substrate/cell ratio were found to have significant influences on the bioresolution properties of G. geotrichum ZJUTZQ200. Based on the bioresolution product (2R,3S)-EPG, taxol’s side chain ethyl (2R,3S)-3-benzoylamino-2-hydroxy-3-phenylpropionate was successfully synthesized by a chemoenzymatic route with high enantioselectivity (e.e.S > 95%).

Chemoenzymatic synthesis of both enantiomers of 3-hydroxy- and 3-amino-3-phenylpropanoic acid

Ethyl (S)-3-hydroxy-3-phenylpropionate (S)-2 was obtained by the asymmetric reduction of ethyl 3-phenyl-3-oxopropionate 1 with the yeast Saccharomyces cerevisiae (ATCC 9080). The kinetic resolution of racemic ethyl 2-acetoxy-3-phenyl-propionate rac-3 with the same microorganism, gave after hydrolysis ethyl (R)- and (S)-3-hydroxy-3-phenylpropionates (R)-2 and (S)-2 which were converted by a straightforward series of reactions to the enantiomers of 3-amino-3-phenyl-propionic acids (S)-6 and (R)-6. The asymmetric reduction and hydrolytic kinetic resolution were also tested with several other whole cell systems under a variety of conditions.

Enzymatic production of Cilastatin intermediate via highly enantioselective hydrolysis of methyl (±)-2,2-dimethylcyclopropane carboxylate using newly isolated Rhodococcus sp. ECU1013

(S)-(+)-2,2-Dimethylcyclopropane carboxylic acid [(S)-(+)-DMCPA] is a key chiral intermediate for production of Cilastatin, an excellent renal dehydropeptidase-I inhibitor. In this study, a new method for preparation of (S)-(+)-DMCPA with microbial esterases was investigated. A microbial screening program obtained six esterase-producing isolates that could display relatively high activities and enantioselectivities using racemic ethyl 2,2-dimethylcyclopropane carboxylate (DMCPE) as screening substrate, aiming at forming optically pure (S)-(+)-DMCPA. Further selection was carried out with substrates having different alcohol moieties, including methyl, ethyl, and 2-chloroethyl esters. Finally, one of these strains, numbered ECU1013, with high enantioselectivity toward the hydrolytic resolution of methyl 2,2-dimethylcyclopropane carboxylate (DMCPM), afforded the (S)-product in 92% ee, and was later identified as Rhodococcus sp. According to our research, there were several active esterases to DMCPM in cells of Rhodococcus sp. ECU1013; however, (S)-preferential esterase was selectively enriched based on the time-dependent profile of esterases biosynthesis, thereby the enantiomeric excess of biotransformation product (ee p) was constantly increased, finally maintained at 95% (S). To improve the yield, various organic solvents were employed for better dispersion of the hydrophobic substrate. As a result, (±)-DMCPM of up to 400mM in the organic phase of isooctane was enantioselectively hydrolyzed into (S)-(+)-DMCPA, with an isolation yield of 38% and a further increase of ee p to 99%.

Enzymatic preparation of (S)-3-amino-3-(o-tolyl)propanoic acid, a key intermediate for the construction of Cathepsin inhibitors

• ( S )-3-Amino-3-( o -tolyl)propanoic acid was prepared in high ee (>98%). • Burkholderia cepacia lipase catalysed enantioselectively ( E > 200) the acylation of N -hydroxymethylated β-lactam and hydrolysis of β-amino ester. • Ring cleavage of β-lactam by using Candida antarctica lipase B showed excellent E (>200). Enantiomerically pure ( S )-3-amino-3-( o -tolyl)propanoic acid [( S )- 6 ], identified as the preferred enantiomeric form for the construction of novel β-amino acid derivatives as inhibitors of Cathepsin, was prepared through both indirect and direct enzymatic strategies. Resolution of hydroxymethylated β-lactam (±)- 1 through Burkholderia cepacia lipase PSIM-catalysed R -selective butyrylation ( E > 200) was first carried out in t -BuOMe. Treatment of the unreacted ( S )-1 with 18% HCl then furnished the desired ( S )- 6 ·HCl. Next, Candida antarctica lipase B catalysed the ring cleavage of racemic 4-( o -tolyl)azetidin-2-one [(±)- 2 ] with excellent R enantioselectivity ( E > 200), either in t -BuOMe with added H 2 O as nucleophile or in H 2 O at 60 °C. Hydrolysis of the less reactive β-lactam enantiomer [( S )- 2 ] with 18% HCl afforded ( S )-6·HCl. A direct enzymatic route to enantiomeric ( S )- 6 was finally optimized through the lipase PSIM-catalysed S -enantioselective ( E > 200) hydrolysis of racemic ethyl 3-amino-3-( o -tolyl)propanoate [(±)- 3 ] in t -BuOMe with added H 2 O at 45 °C or in H 2 O at 3 °C.

Tsukamurella sp. E105 as a new biocatalyst for highly enantioselective hydrolysis of ethyl 2-(2-oxopyrrolidin-1-yl) butyrate

A new bacterial strain, E105, has been introduced as a biocatalyst for the enantioselective hydrolysis of ethyl (R,S)-2-(2-oxopyrrolidin-1-yl) butyrate, (R,S)-1, to (S)-2-(2-oxopyrrolidin-1-yl) butyric acid, (S)-2. This strain was isolated from 60 soil samples using (R,S)-1 as the sole carbon source. The isolate was identified as Tsukamurella tyrosinosolvens E105, based on its morphological characteristics, physiological tests, and 16S rDNA sequence analysis. The process of cell growth and hydrolase production for this strain was then investigated. The hydrolase activity reached its maximum after cultivation at 200rpm and 30°C for 36h. Furthermore, the performance of the enantioselective hydrolysis of (R,S)-1 was studied. The optimal reaction temperature, initial pH, substrate concentration, and concentration of suspended cells were 30°C, 6.8, 10 and 30g/l (DCW), respectively. Under these conditions, a high conversion (>45%) of the product (S)-2 with an excellent enantiomeric excess (ee) (>99%), and a satisfied enantiomeric ratio (E) (>600) as well were obtained. This study showed that the bacterial isolate T. tyrosinosolvens E105 displayed a high enantioselectivity towards the hydrolysis of racemic ethyl 2-(2-oxopyrrolidin-1-yl) butyrate.

ChemInform Abstract: Practical and Scalable Synthesis of Ethyl (R)‐Piperidine‐3‐acetate.

AbstractKey feature of the novel synthesis of ethyl (R)‐piperidine‐3‐acetate is the hydrogenation of N‐benzylpyridinium chloride (I) to afford the racemic ethyl piperidinylacetate (II), which can be kinetically resolved by use of enantiopure mandelic acid.

Kinetic Resolution of Ethyl-2-hydroxy-4-phenylbutyrate with Lipase AK as Catalyst

Ethyl (R)-2-hydroxy-4-phenylbutyrate was prepared by enzyme resolution of racemic ethyl- 2-hydroxy-4-phenylbutyrate. The optimal resolution conditions were 0.074 mol/L ethyl-2-hydroxy-4-phenylbutyrate, 20 mg lipase AK in 2.0 ml ethenylethanoate, 30 0C, 100 rpm. Enantiomeric excess of ethyl (R)-2-hydroxy-4-phenylbutyrate was up to 99%. Kinetic resolution model of ethyl- 2-hydroxy-4-phenylbutyrate by lipase AK was described by double substrate ping-pong mechanism. Model data agreed well with experimental data.

Chemo- and biocatalytic strategies to obtain phenylisoserine, a lateral chain of Taxol by asymmetric reduction

Enriched ethyl 3-benzamido-2-hydroxy-3-phenylpropanoate (protected phenylisoserine), the chiral side chain of Taxol, was obtained via asymmetric reduction with transition metal–diphoshine complexes or with whole cells of non-conventional yeasts. Asymmetric hydrogenation was carried out using different approaches: hydrogenation of the tetra-substituted double bond of (E)-1-benzamido-3-ethoxy-3-oxo-1-phenylprop-1-en-2-yl ethyl oxalate 1 with Ir(I)–diphosphine complexes in the presence of TEA, hydrogenation of the carbonyl group of racemic ethyl 3-benzamido-2-oxo-3-phenylpropanoate 2 with Ru(II)–diphoshine complexes in the presence of a Lewis acid and finally a two-step enzymatic transformation of (E)-1-benzamido-3-ethoxy-3-oxo-1-phenylprop-1-en-2-yl ethyl oxalate 1 catalyzed by whole cells of yeasts bearing cell-bound esterases and dehydrogenases.

A Two-Step Resolution for Preparing Enantiopure (S)-Ethyl Nipecotate

Enantiopure nipecotic acid or ethyl nipecotate are key precursors for synthesizing a variety of pharmaceutically important compounds. In this work a two-step resolution of racemic ethyl nipecotate was developed to prepare enantiopure (S)-ethyl nipecotate. In the enzymatic resolution step, six lipases were screened for their ability to enantioselectively hydrolyze rac-ethyl nipecotate in t-butanol at 30°C and Novozym 435 was found to be the most effective. Solvent effects on the hydrolysis conversion and enantioselectivity showed that water was the optimum medium. When rac-ethyl nipecotate concentration was kept at 0.5M, the hydrolysis under optimum conditions (lipase loading 5mg/mL, phosphate buffer pH 7.0, reaction temperature 30°C, reaction time 6h) afforded 68.9% ees and 69.5% eep at 49.8% conversion. Novozym 435 preferentially hydrolyzed (R)-ethyl nipecotate over (S)-enantiomer. A parallel reaction model was suggested and found to fit the experimental initial rate data very well. (S)-enriched ethyl nipecotate was further resolved using (D)-tartaric acid and enantiopure (S)-ethyl nipecotate (98.5% ee) was acquired in 84.3% yield. The overall yield of enantiopure (S)-ethyl nipecotate by this two-step resolution was up to 36.0%.

Immobilization to improve the properties of Pseudomonas fluorescens lipase for the kinetic resolution of 3-aryl-3-hydroxy esters

Lipase AK “Amano” 20 from Pseudomonas fluorescens (PFL) was immobilized using diverse immobilization techniques. The methods developed, especially the optimized sol–gel procedure, enabled the fine tuning of enzymatic activity and enantioselectivity for the kinetic resolution of racemic ethyl 3-aryl-3-hydroxypropanoates. The aryl moieties of the racemates include furan-2 and 3-yl, thiophen-2 and 3-yl, benzofuran-2-yl, benzo[ b]thiophen-2-yl, as well as phenyl and 4-chloro- and 4-methoxyphenyl groups. The optimized PFL sol–gel preparation (encapsulation from the aqueous solution of PFL, sucrose and Celite in situ) was shown to be efficiently reusable in ten cycles and highly enantioselective with E > 200 to all other substrates except furan-2 and 3-yl and thiophen-2 and 3-yl substituted compounds with E 108–184.

Syntheses and Characterization of Copper(II) Carboxylate Dimers Formed from Enantiopure Ligands Containing a Strong π···π Stacking Synthon: Enantioselective Single-Crystal to Single-Crystal Gas/Solid-Mediated Transformations

Tri- and tetrafunctional enantiopure ligands have been prepared from 1,8-naphthalic anhydride and the amino acids L-alanine, D-phenylglycine, and L-asparagine to produce (S)-2-(1,8-naphthalimido)propanoic acid (HL(ala)), (R)-2-(1,8-naphthalimido)-2-phenylacetic acid (HL(phg)), and (S)-4-amino-2-(1,8 naphthalimido)-4-oxobutanoic acid (HL(asn)), respectively. Reactions of L(ala)(-) with copper(II) acetate under a variety of solvent conditions has led to the formation and characterization by X-ray crystallography of three similar copper(II) paddlewheel complexes with different axial ligands, [Cu(2)(L(ala))(4)(THF)(2)] (1), [Cu(2)(L(ala))(4)(HL(ala))] (2), and [Cu(2)(L(ala))(4)(py)(THF)] (3). A similar reaction using THF and L(phg)(-) leads to the formation of [Cu(2)(L(phg))(4)(THF)(2)] (4). With the exception of a disordered component in the structure of 4, the naphthalimide groups in all of these compounds are arranged on the same side of the square, central paddlewheel unit, forming what is known as the chiral crown configuration. A variety of π···π stacking interactions of the 1,8-naphthalimide groups organize all of these complexes into supramolecular structures. The addition of the amide group functionality in the L(asn)(-) ligand leads to the formation of tetrameric [Cu(4)(L(asn))(8)(py)(MeOH)] (5), where reciprocal axial coordination of one of the amide carbonyl oxygen atoms between two dimers leads to the tetramer. Extensive supramolecular interactions in 5, mainly the π···π stacking interactions of the 1,8-naphthalimide supramolecular synthon, support an open three-dimensional structure containing large pores filled with solvent. When crystals of [Cu(4)(L(asn))(8)(py)(MeOH)] are exposed to (S)-ethyl lactate vapor, the coordinated methanol molecule is replaced by (S)-ethyl lactate, bonding to the copper ion through the carbonyl oxygen, yielding [Cu(4)(L(asn))(8)(py)((S)-ethyl lactate)] (6) without a loss of crystallinity. With the exception of the replacement of the one axial ligand, the molecular structures of 5 and 6 are very similar. In a similar experiment of 5 with vapors of (R)-ethyl lactate, again a change occurs without a loss of crystallinity, but in this case the (R)-ethyl lactate displaces only slightly more than half of the axial methanol molecules forming [Cu(4)(L(asn))(8)(py){((R)-ethyl lactate)(0.58)(MeOH)(0.42)}] (7). Importantly, in 7, the (R)-ethyl lactate coordinates through the hydroxyl group. When crystals of [Cu(4)(L(asn))(8)(py)(MeOH)] are exposed to vapors of racemic ethyl lactate, the coordinated methanol molecule is displaced without a loss of crystallinity exclusively by (S)-ethyl lactate, yielding a new form of the tetramer [Cu(4)(L(asn))(8)(py)((S)-ethyl lactate)], in which the ethyl lactate in the pocket bonds to the copper(II) ion through the carbonyl oxygen as with 6. Exposure of [Cu(4)(L(asn))(8)(py){((R)-ethyl lactate)(0.58)(MeOH)(0.42)}] to racemic ethyl lactate yields a third form of [Cu(4)(L(asn))(8)(py)((S)-ethyl lactate)], where the three forms of [Cu(4)(L(asn))(8)(py)((S)-ethyl lactate)] have differences in the number of ordered (S)-ethyl lactate molecules located in the interstitial sites. These results demonstrate enantioselective bonding to a metal center in the chiral pocket of both 5 and 7 during single-crystal to single-crystal gas/solid-mediated exchange reactions.