Enzymatic resolution of racemic secondary cyclic allylic alcohols

The resolutions of five racemic cyclic alcohols: 6,6-dimethylcyclohex-2-en-1-ol (±)-5, 4,4-dimethylcyclohex-2-en-1-ol (±)-7, 5,5-dimethylcyclohex-2-en-1-ol (±)-11 and isomeric trans-(±)-13 and cis-piperitols (±)-14 are presented. They were resolved by enzymatic esterification with vinyl esters or by enzymatic hydrolysis of their racemic esters in phosphate buffer. The following lipases were used as biocatalysts: Novozyme 435 (Candida antarctica), Amano PS (Burkholderia cepacia) and lipase from Candida cylindracea. All isomers of alcohols were obtained with at least 96% ee.     

2-Methoxy-2-(1-naphthyl)propionic acid,a powerful chiral auxiliary for enantioresolution of alcohols and determination of their absolute configurations by the 1H NMR anisotropy method

Racemic 2-methoxy-2-(1-naphthyl)propionic acid (1, MαNP acid) was enantioresolved as its esters derived from various chiral alcohols. For example, a diastereomeric mixture of esters prepared from (±)-1 and (1R,3R,4S)-(−)-menthol was easily separated by HPLC on silica gel yielding esters (−)-2a and (−)-2b, the separation factor α=1.83 being unusually large. The ¹H NMR chemical shift differences, Δδ=δ(R)–δ(S), between diastereomers 2a and 2b, are much larger than those of conventional chiral auxiliaries, e.g. Mosher’s MTPA and Trost’s MPA acids. This acid 1 is therefore very powerful for determining the absolute configuration of chiral alcohols by the ¹H NMR anisotropy method. Solvolysis of the separated esters yielded enantiopure acids (S)-(+)-1 and (R)-(−)-1, which are useful for enantioresolution of racemic alcohols.     

Resolution of C2-symmetric 2,3-diphenylbutane-1,4-diol and purification of diastereomeric 1,4-diphenylbutane-1,4-diol using (S)-proline and boric acid

Racemic 2,3-diphenylbutane-1,4-diol (±)-1 is resolved to obtain the corresponding (R,R)-isomer in 98% e.e. through reaction with (S)-proline and boric acid. Partially resolved (R,R)-(−)-1 and (S,S)-(+)-1 have been enriched to obtain samples of 95 and 97% e.e. through reaction with (S)-proline and boric acid. Diastereomeric 1,4-diphenylbutane-1,4-diol 2 has been purified to obtain the (R,R)-isomer in 98% e.e. using (S)-proline and boric acid.     

Asymmetric allylation of aldehydes with allyltrichlorosilane using aza-paracyclophane-oxazoline-N-oxide catalysts

Novel aza-paracyclophane-oxazoline catalysts 4, 5 were produced from Vögtle’s R_p-2-cyano-aza-paraclycophane and amino alcohols reacted with zinc chloride followed by m-chloroperbenzoic acid. 4′-Benzyl and tert-butyl-S and R-oxazoline variants were produced and explored as catalysts for asymmetric allylation of aldehydes using trichloroallylsilane. With R_p,S-4a (R = tert-butyl) (1.5 mol %) aromatic aldehydes reacted with high yields and selectivities, as with benzaldehyde (95%, 93% ee). R_p,S-4b (R = benzyl) was superior with dihydrocinnamaldehyde (77%, 85% ee).     

One-pot preparation of Julia-Kocienski sulfides and sulfones from alcohols

A method for one-pot preparation of Julia-Kocienski sulfides and sulfones from alcohols and thiols is reported. A variety of primary alcohols were converted to the corresponding mesylates by methansulfonyl chloride and triethylamine in THF. After the reaction is complete, thiol (1 or 10) and either NaH or t-BuOK were added. The Julia-Kocienski sulfides 3, 9 and 11 were prepared by one-pot two steps procedure from alcohols in 76–96% yields (16 examples). Furthermore, after the sulfide formation, the reaction mixture was neutralized by p-toluenesulfonic acid and treated with H₂O₂ and ammonium molybdate in EtOH to give the Julia-Kocienski sulfones 4 in good yields except for trans-2-hexen-1-ol.     

Thioester-assisted α-sialylation reaction

α-Selective sialylation reactions were carried out using novel sialic acid building blocks that possess a thioester auxiliary. In contrast to other arylthio- and benzylthioester derivatives, sialyl phosphite 1a (with the phenylthioester moiety) was employed as the α-selective building block, and was reacted with various primary alcohols, including the C6-OH group of galactose and glucose, with moderate to excellent α-selectivities. For C3-OH of the galactose, 4,6-di-O-benzylgalactal afforded desired α-linkage with excellent selectivity.     

A general method for the synthesis of enantiopure aliphatic chain alcohols with established absolute configurations. Part 1. Application of the MαNP acid method to acetylene alcohols

A method using (S)-(+)-2-methoxy-2-(1-naphthyl)propionic acid 1 (MαNP acid) has been applied to acetylene alcohols 4–14 to determine their absolute configurations by ¹H NMR anisotropy and/or X-ray crystallography. Diastereomeric MαNP esters prepared from racemic acetylene alcohols and (S)-(+)-MαNP acid 1 were easily separable by HPLC on silica gel. From the ¹H NMR anisotropy Δδ data of separated diastereomeric MαNP esters {Δδ = δ (R,X) − δ(S,X) = δ(2nd fr.) − δ(1st fr.)}, the absolute configurations of the first eluted esters were determined. This MαNP acid method has been successfully applied to various acetylene alcohols 4–12 and 14. In the case of MαNP esters 21b, 24a, and 26a, their absolute configurations were unambiguously determined by X-ray crystallography, which confirmed the absolute configuration assignments performed by ¹H NMR anisotropy. These acetylene alcohol MαNP esters can serve as key intermediates for the synthesis of enantiopure aliphatic chain alcohols with established absolute configurations as described in Part 2 of this series.     

Resolution and absolute configuration of dimethyl hydroxy-(ferrocenylmethyl)phosphonate

Racemic dimethyl hydroxy-(ferrocenylmethyl)phosphonate rac-1 was resolved via the formation of diastereomeric esters with (S)-α-methoxy-α-phenylacetic acid. The diastereomers, separated by column chromatography, were stereospecifically hydrolyzed by dissolution in trifluoroacetic acid at −30 °C and quenching with water. The absolute configuration of one enantiomer of 1 was assigned by X-ray diffraction.     

Functionalization of C60 via organometallic reagents

The reaction of [60]fullerene with organolithium and Grignard reagents carrying orthoester, acetal or other end groups yielded adducts 3-5 at the 6-6 bond of C60 after quenching with trifluoroacetic acid. The adducts could be easily methylated or benzylated with methyl iodide or benzyl bromide in the presence of potassium tert-butoxide to yield exclusively the 1,4-disubstituted C60 6 and 7a,b. Cleavage of the orthoester, acetal and silylether groups gave the corresponding carboxylic acid 9, aldehydes 10a,b and 11 and alcohols 12 and 13a,b. The carboxylic acid 9 readily reacted with alanine ethyl ester under standard peptide coupling conditions to give 14 in 55% yield. Attempts to generate a silyl enol ether from the reaction of aldehyde 10b with TIPSOTf and triethylamine failed. Instead the reaction led to a cyclized ether 16a (or alcohol 16b in the absence of silylating agent) resulting from the addition of an initially formed fulleride anion to the aldehyde group. The corresponding acetal 4b reacted similarly. The reaction of aldehyde 10b with aniline also gave a cyclized product 19. Surprisingly, aldehyde 11, which no longer carried an acidic fullerene proton reacted with aniline to give a product 20 resulting from an intramolecular Diels-Alder reaction followed by aromatization of a primarily formed N-phenylimine. Alcohol 13b could be readily converted to the corresponding bromide using tetramethyl-α-bromoenamine. The bromide was reacted with the carbanion derived from the protected glycine derivative to yield the diastereomeric fullerene amino acid derivatives 1-benzyl-4-[α-propyl-tert-butylglycinate benzophenone imine] 1,4-dihydro[60]fullerenes 24a and 24b.     

Kinetic studies and improved reaction conditions for the halogen shift rearrangments of aryldihalopropanols

Solvolytic data were obtained from the acid catalyzed trifluoroacetolysis of 1-(o-chlorophenyl)-2,2-dichloro-1-propyl trifluoroacetate (1a-TFA) and the analogous 2,2-dibromo trifluoroacetate 1b-TFA which implicate a halonium ion intermediate in the rearrangement to an α-haloketone. Employing the conditions used to achieve kinetic control, substantial increases in yield were realized for those compounds which reacted too rapidly in and were unstable to concentrated sulfuric acid (i.e. 1b and 1c).     

Stereoselective oxazaborolidine–borane reduction of biphenyl alkyl diketones–lignin models: enantiopure dehydrodiapocynol derivatives

Asymmetric reduction of two conformationally flexible biphenyl alkyl diketones 9 and 10 with (R)-oxazaborolidine 3-borane system was successfully carried out and the corresponding biphenyl alcohols 11 and 12 were obtained in high yield and e.e. with predominance of the homochiral (S,S) dicarbinols. The absolute configuration of diastereopure dehydrodiapocynol derivative (S,S)-14 was assigned by crystallographic analysis which confirms the known stereochemical course of CBS-catalysed reduction of ketones and gives useful information on spatial arrangement.     

The influence of microwave irradiation on lipase-catalyzed kinetic resolution of racemic secondary alcohols

The influence of microwave irradiation on the Novozyme 435^® (Candida antarctica lipase) catalyzed kinetic resolution of secondary alcohols with different functional groups was studied in comparison to the use of conventional heating at 60 °C. p-Chlorophenyl acetate was used as an acyl donor and toluene as the solvent. (±)-1-Phenyl-1-propanol 1, (±)-1-(4-bromophenyl)-propan-1-ol 3, (±)-1-phenylbut-3-en-1-ol 5 and (±)-3-bromo-2-(2-hydroxypropyl)-1,4-dimethoxynaphthalene 7 were successfully resolved into their (S)-alcohols and (R)-esters, respectively, in good enantiomeric excess. Resolution of (±)-ethyl-5-(4-methoxybenyloxy)-3-hydroxypentanoate 9 afforded its (R)-alcohol and (S)-ester using this method. In addition, microwave-assisted lipase transesterification of meso-symmetric diol 11 effected desymmetrization to ester 12 with high enantiomeric excess. In all cases studied, the conversion value for the microwave-assisted lipase kinetic resolution of secondary alcohols was higher than that obtained using conventional heating.     

Synthesis and chiral recognition abilities of new calix[6]arenes bearing amino alcohol moieties

Herein the synthesis and recognition abilities towards amino acids and amino alcohols of new d-/l-phenylalaninol substituted p-tert-butylcalix[6]arenas are reported. These compounds, 6 and 7 have been synthesized via nucleophilic substitution reactions involving 5,11,17,23,29,35-tert-butyl-37,38-dimethoxy-39,40,41,42-(p-tosylethoxy)calix[6]arene 5 with d-/l-phenylalaninol in dry THF. The extraction properties of 6 and 7 towards some selected amino acid methylesters and amino alcohols have been studied by liquid–liquid extraction. These results show that chiral calix[6]arene derivatives exhibit a good affinity towards all amino acids and amino alcohols.     

Reversal of enantioselectivity by adding Ti(OiPr)4: novel sulfamide-amine alcohol ligands for the catalytic asymmetric addition of diethylzinc to aldehydes

Novel sulfamide-amine alcohol ligands (6) derived from (−)-ephedrine (4a) and (+)-pseudoephedrine (4b) with multiple stereogenic centers were applied to the catalytic asymmetric addition of diethylzinc to aldehydes, providing (S)-products in high yields and good enantioselectivities. These sulfamide-amine alcohols together with Ti(OⁱPr)₄ were shown to obtain the (R)-products in significant enantiomeric excesses (e.e.) and high yields. In addition, sulfamide-amine alcohols were superior to the original chiral sources 4a and 4b, which afforded no enantioselectivity in the Ti(OⁱPr)₄-mediated reaction.     

Construction,molecular docking,antimicrobial and antioxidant activity of some novel 3-substitued indole derivatives using 3-Acetyl indole

This dissertation presents a method for the synthesis of substituted indoles bearing heterocyclic substituent in the 3- position. The route for the synthesis of the heterocyclic substituents indoles starts from the 3-acetyl indole nucleus. The reaction of 3-acetyl indole 1 with hydrazide compounds such as phenylhydrazine, hydrazine hydrate, and thio-semicarbazide, yields 3-(1-(2-phenylhydrazono) ethyl)-1H-indole 2, 3-(1-hydrazonoethyl)-1H-indole 6, and thiosemicarbazone 10, respectively. Thiophene-2-carboxaldeyde, isatine and 3-acetyl indole reacted with 3-(1-Hydrazonoethyl)-1H-indole 6. In the same way, 3-(1-(2-phenylhydrazono) ethyl)-1H-indole 2 reacted with thioglycollic acid, glycine and benzaldehyde. Thiosemicarbazone 10 reacted smoothly with acetic anhydride, piperidine, concentration of hydrochloric acid and thiophene-2-carboxaldeyde to provide the corresponding heterocycles. The reaction of 3-acetyl indole 1 with amine compounds such as p-nitroaniline formed Schiff base 15, which reacted with thioglycollic acid to give compound 16. 3-Acetyl indole 1 reacted with ethylene diamine to afford bis imine indole 17. The reports of the docking study revealed that the new compounds exhibit good antibacterial activity. The synthesized compounds screened in vitro for their antibacterial activity revealed remarkable inhibitory effects on the selected microorganisms. Besides, the antioxidant activity of some newly designed compounds has been investigated. The structures of the newly synthesized compounds are examined by spectral data (IR, ¹HNMR, ¹³C NMR and mass spectra).     

A scalable synthesis of (R)-3-(2-aminopropyl)-7-benzyloxyindole via resolution

(±)-3-(2-Aminopropyl)-7-benzyloxyindole 1, assembled from 7-benzyloxyindole 3 in 59% overall yield, is resolved with O,O′-di-p-toluoyl l-(2R,3R)-tartaric acid 7 into (R)-1, a key intermediate of AJ-9677 2 (selective adrenaline β₃-agonist) in 99.5% e.e. and 36% overall yield. The unwanted enantiomer (S)-1 (61.9% e.e.; recovered in 57% yield from the crystallization filtrate) can be reused in another round of resolution after its enantiomeric purity is lowered to 3.7% by Raney Co treatment under a hydrogen atmosphere.     

Synthesis and application in enantioselective hydrogenation of new free and chromium complexed aminophosphine–phosphinite ligands

A straightforward synthesis of new free and Cr(CO)₃ complexed AMPP ligands (4–7) is described starting from (S)-indoline-2-carboxylic acid. The ligands were applied successfully in the asymmetric hydrogenation of α-functionalized ketones i.e. a ketolactone 8, a ketoamide 9 and an aminoketone 10 leading to the corresponding optically active alcohols in 99, 97, and 99% ee respectively.     

Enzyme-catalysed kinetic resolution of N,O-diacetyl derivatives of cyclic 1,3-amino alcohols

Racemates of N,O-diacetyl derivatives of cis- and trans-2-aminomethylcyclopentanols 5 and 6 and cis- and trans-2-aminomethylcyclohexanols 7 and 8 were resolved through lipase-catalysed asymmetric O-deacylation at the (1R) stereogenic centre. The gram-scale resolutions of 5–8 were carried out with ethanol in di-iso-propyl ether in the presence of Novozym 435. The unreacted N,O-diacetyl compounds 5a–8a were transformed to the corresponding alcohols 5c–8c without loss of enantiopurity.     

Biocatalytic syntheses of chiral non-racemic 2-hydroxyalkanephosphonates

A series of 2-oxoalkanephosphonates 2 were screened for reduction with Geotrichum candidum. Only diethyl 2-oxopropanephosphonate 2a underwent asymmetric reduction to give (+)-(R)-diethyl 2-hydroxypropanephosphonate 3a with 98% e.e. In turn, a series of racemic 2-hydroxyalkanephosphonates 3 were acetylated under kinetic resolution conditions in the presence of various lipases to give the corresponding 2-acetoxyalkanephosphonates 4 and recovered alcohols 3 in good yields and with e.e. up to 93%.     

Enzymatic resolution of (±)-2-(Nβ-t-butoxycarbonyl-Nα-methylhydrazino)cycloalkanols

Racemates of cis- and trans-2-(N_β-t-butoxycarbonyl-N_α-methylhydrazino)cyclopentanols and -cyclohexanols 1–4 were resolved through lipase PS- or Novozym 435-catalysed asymmetric acylation of the secondary OH group at the (R)-stereogenic centre. High enantioselectivity (E >200) was observed when vinyl acetate or vinyl butyrate was used in diisopropyl ether, resulting in the enantiopure hydrazino esters 1a–4a and hydrazino alcohols 1b–4b. Methanolysis of the esters 1a–4a afforded the corresponding 2-hydrazinocycloalkanols 1c–4c (ee usually >95%).