Preparation of single-enantiomer 2-methyl-4-heptanol, a pheromone of Metamasius hemipterus, using (S)-2-methoxy-2-(1-naphthyl)propionic acid

To investigate the resolution of secondary alcohols using 2-methoxy-2-(1-naphthyl)propionic acid (MalphaNP acid), 2-methyl-4-heptanol, one of the aggregation pheromones of Metamasius hemipterus, was resolved using (S)-MalphaNP acid. As a chiral-resolving agent, MalphaNP acid is superior to 3,3,3-trifluoro-2-methoxy-2-phenylpropionic acid (MTPA) in terms of HPLC separation and NMR shielding. A better separation of diastereomeric MalphaNP esters was observed when n-hexane-THF was used as the eluent for silica gel HPLC. The solvolysis of the diastereomeric MalphaNP esters gave (R)-2-methyl-4-heptanol and its enantiomer; enantiopure (S)-MalphaNP acid was also recovered. In addition, the preferred conformation of the MalphaNP ester was confirmed using methyl (R)-3-hydroxyvalerate as an authentic compound.     

High-performance liquid chromatographic separation of the enantiomers of anti-inflammatory 2-arylpropionates: suitability of the method for in vitro metabolic studies

The enantiomers of 2-phenylpropionic acid, 2-(2-naphthyl)propionic acid, 2-(4-biphenyl)propionic acid and six anti-inflammatory congeners were separated by high-performance liquid chromatography via their diastereoisomeric derivatives with (S)-(-)-1-phenylethylamine. In agreement with a general rule, the diastereoisomers derived from the (R)-acids are less polar and elute first. Structural factors influencing the resolution are discussed. Good calibrations were obtained for R/S ratios and total (R + S) concentrations of flurbiprofen and naproxen added to inactivated rat liver preparations. The method is suitable for in vitro metabolic studies of chiral 2-arylpropionates.     

Total synthesis of (-)-dihydrocelacinnine and (d-celabenzine

(S)-3-amino-3-phenylpropionic acid, as an intermediate, was converted to dihydrocelacinnine and celabenzine.     

Convenient syntheses of 7-hydroxy-1-(hydroxymethyl)-3-(thymin-1-yl)-2,5-dioxabicyclo

Synthesis of the diastereoisomeric LNA (locked nucleic acid) nucleosides 1-(2-O,4-C-methylene-alpha-L-ribofuranosyl)thymine (6) and 1-(2-O,4-C-methylene-alpha-L-xylofuranosyl)thymine (13) are reported via convenient reaction cascades from di-O-p-toluenesulfonyl and tri-O-methanesulfonyl nucleoside derivatives 3, 7, and 10.     

1-Benzotriazol-1-yl-3,3,3-trifluoro-2-methoxy-2- phenylpropan-1-ones: Mosher-Bt reagents

Benzotriazole derivatives of 3,3,3-trifluoro-2-methoxy-2-phenylpropionic acid react with water-soluble amino acids and peptides in an acetonitrile/water (2:1) mixture to give the corresponding amides in quantitative yield.     

Synthesis of some 7-α-carboxyethyl-1,3-dihydro-(2H)-1,4-benzodiazepin-2-ones

1,4-Benzodiazepin-2-ones possessing an α-carboxyethyl group in 7-position (21-25) were prepared from a key compound, 2-amino-5-α-carboxyethylbenzophenone (8) or from its O-benzyl derivative 14 , using methods developed previously. An optimized route to 8 starting from 2-nitro-5-chlorobenzophenone ( 1 ), as well as some unsuccessful attempts are described. Compound 8 was deaminated into racemic α-(3-benzoyl)-phenylpropionic acid ( 9 ), a well-known antiinflammatory agent.     

Synthesis of enantiomeric (+)- and (-)-6-(1-methylethylidene)-3,3a,6,6a-tetrahydro-2H-cyclopenta[b]furan-1-ones

Baeyer-Villiger oxidation of racemic [2 +2 ]-cycloadduct derived from dichloroketene and dimethylfulvene gave 3,3-dichloro-6-(1-methylidene)-3,3a,6,6a-tetrahydro-2H-cyclopenta[b]furan-2-one, and opening of the lactone ring in the latter with (+)-α-methylbenzylamine produced diastereoisomeric amides which can be readily separated by chromatography on silica gel. The subsequent lactonization and reductive dechlorination afforded enantiomeric (?)- and (+)-6-(propan-2-ylidene)-3,3a,6,6a-tetrahydro-2H-cyclopenta[b]-furan-1-ones.     

Extended application of a chiral stationary phase based on (+)-(1 8-crown-6)-2,3,11,12-tetracarboxylic acid to the resolution of N-(substituted benzoyl)-alpha-amino acid amides

A chiral stationary phase (CSP 1) based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid was applied to the resolution of N-(substituted benzoyl)-alpha-amino acid amides and esters. N-(Substituted benzoyl)-alpha-amino acid amides were well resolved using a mixture of acetic acid-triethylamine-acetonitrile (0.01:0.05:100, v/v/v) as an optimum mobile phase while N-(substituted benzoyl)-alpha-amino acid esters were not resolved at all. In contrast, both N-(substituted benzoyl)-alpha-amino acid amides and esters were not resolved at all or resolved very poorly on another CSP (CSP 2), which lacks the two N-H hydrogens of the amide tethers of CSP 1. Among the substituents on the benzoyl group of analytes, the nitro group was the best for good resolution of analytes on CSP 1. From these results, the two N-H hydrogens of the amide tethers of CSP 1, the carbonyl oxygen of the amide group of analytes, and the nitro group on the benzoyl group of analytes were concluded to play significant roles in chiral recognition. In addition, various N-(3,5-dinitrobenzoyl)leucine amides with different lengths of N-alkylamide chains were resolved on CSP 1 and N-(3,5-dinitrobenzoyl) leucine N-propylamide was found to show the best chiral recognition in terms of the separation (alpha = 1.30) and the resolution factor (Rs= 3.17).     

Metal-dependent reactions of bulky metal(II) amides M[N(SiMe3)2]2 with 3,3'-disubstituted binaphthols (HO)2C20H10(SiR3)2-3,3': selective conversion of one equivalent -OH group to a silyl ether -OSiMe3

The outcome of the reaction of the bulky metal(II) amides M[N(SiMe3)2]2. nTHF (M = Be, Zn, Ge, Sn, n = 0; M = Mg, Ca, n = 2) with (R)-3,3'-bis(trimethylsilyl)-1,1'-bi-2,2'-naphthol ((R)-1) or (S)-3,3'-bis(dimethylphenylsilyl)-1,1'-bi-2,2'-naphthol ((S)-9) depends on the identity of the metal and the nature of the 3,3'-substituents. When M = Be, Zn, or Ge, these amides serve as useful silylation agents that convert only one of the equivalent hydroxyl groups of the binaphthol (R)-1 to a trimethylsilyl ether, whereas the reactions of (R)-1 with the Mg, Ca, or Sn amides generate a polynuclear complex. The reaction pathway for these interconversions was qualitatively monitored using NMR ((1)H and (9)Be) spectroscopy. Treatment of Ge[N(SiMe3)2] 2 with (S)-9 yields both a silyl ether and the chelated germanium(II) binaphthoxide (S)-[Ge{O2C20H10(SiMe2Ph)2-3,3'}{NH3}], which was structurally characterized.     

Toward the development of a structurally novel class of chiral auxiliaries: diastereoselective aldol reactions of a (1R,2S)-ephedrine-based 3,4,5,6-tetrahydro-2H-1,3,4-oxadiazin-2-one

[reaction: see text] Asymmetric aldol addition reactions have been conducted with (1R,2S)-ephedrine-derived 3,4,5,6-tetrahydro-2H-1,3,4-oxadiazin-2-one (2). Diastereoselectivities range from 75:25 to 99:1 for the formation of the crude non-Evans syn adducts 8a-h. The facial selectivity of the enolate is directed by the stereogenic N(4)-methyl substituent. Aldol adduct 8a is readily cleaved by acid hydrolysis to afford (2S,3S)-3-hydroxy-2-methyl-3-phenylpropionic acid (9) in >95% ee.     

Optically active antifungal azoles. XIII. Synthesis of stereoisomers and metabolites of 1-[(1R,2R)-2-(2,4-difluorophenyl)-2-hydroxy-1-methyl-3-(1H-1,2,4-triazol-1-yl)propyl]-3-[4-(1H-1-tetrazolyl)phenyl]-2-imidazolidinone (TAK-456)

1-[(1R,2R)-2-(2,4-Difluorophenyl)-2-hydroxy-1-methyl-3-(1H-1,2,4-triazol-1-yl)propyl]-3-[4-(1H-1-tetrazolyl)phenyl]-2-imidazolidinone [(1R,2R)-1: TAK-456] is a new antifungal agent selected as a candidate for clinical trials. The three stereoisomers [(1S,2R)-, (1S,2S)- and (1R,2S)-1] of this compound were prepared as authentic samples to determine the enantiomeric and diastereomeric purity of TAK-456 as well as to compare their in vitro antifungal activity. Pharmacokinetic studies of TAK-456 using rats identified the existence of metabolites in the liver homogenate. The structures of the major metabolites were assigned as 4-hydroxy-2-imidazolidinone (3) and/or 5-hydroxy-2-imidazolidinone (4), based on HPLC and LC/MS/MS analyses. These hydroxylated compounds, 3 and 4, were prepared by reduction of the corresponding imidazolidinediones, 11 and 12, and confirmed to be identical to the metabolites by HPLC. In vitro antifungal activities of the three stereoisomers and the synthesized metabolites were considerably weaker than TAK-456.     

Favorskii Rearrangement in the Reaction of 3-(1-Adamantyl)-1-chloro-2-propanone with Amines

The reaction of 3-(1-adamantyl)-1-chloro-2-propanone with amines [diethylamine, (1-adamantyl)methylamine, p-toluidine, and piperidine] in diethyl ether at room temperature involves the Favorskii rearrangement and yields N,N-disubstituted amides of 3-(1-adamantyl)propanoic acid.     

Solution-phase synthesis of a combinatorial library of 3-[4-(coumarin-3-yl)-1,3-thiazol-2-ylcarbamoyl]propanoic acid amides

The parallel solution-phase synthesis of a new combinatorial library of 3-[4-(R1-coumarin-3-yl)-1,3-thiazol-2-ylcarbamoyl]propanoic acid amides 9 has been developed. The synthesis involves two steps: 1) the synthesis of core building blocks - 3- [4-(coumarin-3-yl)-1,3-thiazol-2-ylcarbamoyl]propanoic acids, 6 - by the reaction of 3-(omega-bromacetyl)coumarins 1 with 3-amino(thioxo)methylcarbamoylpropanoic acid (5); 2) the synthesis of the corresponding 3-[4-(coumarin-3-yl)-1,3-thiazol-2-yl- carbamoyl]propanoic acids amides 9 using 1,1'-carbonyldimidazole as a coupling reagent. The advantages of the method compared to existing ones are discussed.     

The Williamson Reaction: A New and Efficient Method for the Alternate Resolution of 2,2'-Bis(bromomethyl)-1,1'-binaphthyl and 1,1'-Binaphthalene-2,2'-diol

Treatment of 2,2'-bis(bromomethyl)-1,1'-binaphthyl [(R,S)-2] with 1,1'-binaphthalene-2,2'-diol (+)-(R)-1 and cesium or potassium carbonate in refluxing acetone, gave the diastereoisomeric dioxacyclophanes (-)-(R,S)-3a and (+)-(R,R)-3b, both obtained in high yield, and the cyclic tetraether (+)-(R,R,R,S)-4 as isolated side product. Boron tribomide-promoted ether cleavage of 3a and 3b gave optically pure (-)-(S)-2 and (+)-(R)-2, respectively, and the recovered diol (+)-(R)-1. Alternatively, the same reaction sequence furnished the resolved diols (-)-(S)-1 and (+)-(R)-1 from (R,S)-1 and (+)-(R)-2, as well as optically pure 2,2'-bis(chloromethyl)-1,1'-binaphthyl (+)-(R)-5 from the racemic dibromide (R,S)-2 by using boron trichloride for ether cleavage.     

Stereoselective Formation of Ternary Copper(II) Complexes of (S)-Amino-acid Amides and (R)- or (S)-Histidine and (R)- or (S)-Tyrosine in Aqueous Solution

Formation constants of ternary complexes of Cu^II with (S)-amino-acid amides ((S)-phenylalaninamide, (S)-prolinamide, and (S)-tryptophanamide) and (R)- or (S)-histidine and (R)- or (S)-tyrosine were determined potentiometrically in aqueous solution. Significant stereoselectivity was presented by all three amides towards histidine, the diastereoisomeric complexes with ‘heterochiral’ ligands being more stable than those with ‘homochiral’ ligands (see Table 3). The stereoselectivity observed with (S)-phenylalaninamide and (S)-tryptophanamide may be explained on the basis of hydrophobic stacking interactions between 1H-imidazole and the aromatic side chain, favoured by the terdentate behaviour of histidine (see Fig.2), whereas repulsive effects seem to be prevalent with (S)-prolinamide. Only (S)-prolinamide and (S)-phenylalaninamide show appreciable stereoselectivity with tyrosine, which is bidentate, probably on account of repulsive interactions. The present results on the stability of ternary complexes in solution allow to draw some conclusions on the mechanism of chiral discrimination performed by Cu^II complexes of (S)-amino-acid amides added to the mobile phase in HPLC (reversed phase).     

Preparation and Applications of Xanthenylamide (XAL) Handles for Solid-Phase Synthesis of C-Terminal Peptide Amides under Particularly Mild Conditions(1-3)

[[9-[(9-Fluorenylmethyloxycarbonyl)amino]xanthen-2(or 3)-yl]oxy]alkanoic acid (XAL) handles have been prepared by efficient four-step routes from 2- or 3-hydroxyxanthone and coupled onto a range of amino-functionalized supports. The resultant XAL supports are the starting points for solid-phase peptide synthesis by Fmoc chemistry. Upon completion of chain assembly, C-terminal peptide amides are released in excellent yields and purities by use of low concentrations [1-5% (v/v)] of trifluoroacetic acid (TFA) in dichloromethane, often without a need for added carbocation scavengers. These cleavage conditions allow retention of all or a significant portion of tert-butyl type and related side-chain protecting groups, which subsequently may be removed fully in a solution process carried out at higher acid concentration. XAL supports are particularly useful for the synthesis of acid-sensitive peptides, including tryptophan-containing sequences that are known to be susceptible to yield- and/or purity-reducing alkylation side reactions. The effectiveness of this chemistry was shown with the syntheses of prothrombin (1-9), acyl carrier protein (65-74), Tabanus atratus adipokinetic hormone, fragments of the protein RHK 1, CCK-8 sulfate, and oxytocin. Furthermore, the application of XAL supports for the preparation of fully protected peptide amides has been demonstrated.     

Total Synthesis of (+)-(8S,13R)-Cyclocelabenzine

An asymmetric synthesis of the spermidine alkaloid (+)-cyclocelabenzine ( 1a ) and its (?)-(13S)-epimer 1b is described using optically active (+)-(3S)-3-amino-3-phenylpropionic acid as the chiral building block. The isoquinolin-1-one fragment 15 was synthesized by a modified Bischler-Napieralski reaction. The relative configuration of the (?)-isomer was determined by an X-ray crystal-structure analysis, which enabled us to determine the absolute configuration of natural (+)- 1a as (8S,13R).     

Determination of the enantiomeric composition of ibuprofen in human plasma by high-performance liquid chromatography

A normal-phase high-performance liquid chromatographic method, using a hexane-ethyl acetate solvent system, for the determination of the enantiomeric composition of ibuprofen in human plasma is described. The method is based on the resolution of the diastereoisomeric amides formed on reaction of the ibuprofen enantiomers with S-1-(naphthen-1-yl)ethylamine using p-chlorophenoxy-acetic acid as internal standard. The application of the method for the determination of the enantiomeric composition of ibuprofen in human plasma following the repeated oral administration of the drug to two volunteers is reported. The plasma concentrations of the S-(+) enantiomer were always greater than that of the R-(-), the ratio of the areas under the enantiomer plasma concentration-time curves (S/R) being 1.8 and 1.6.     

Nitrile biotransformations for highly enantioselective synthesis of oxiranecarboxamides with tertiary and quaternary stereocenters; efficient chemoenzymatic approaches to enantiopure alpha-methylated serine and isoserine derivatives

[reaction: see text] Biotransformations of a number of differently substituted and configured oxiranecarbonitriles using Rhodococcus sp. AJ270, a microbial whole-cell catalyst that contains nitrile hydratase/amidase, were studied. While almost all trans-configured 3-aryl-2-methyloxiranecarbonitriles and 2,3-dimethyl-3-phenyloxiranecarbonitrile were efficiently hydrated by the action of the less enantioselective nitrile hydratase, the amidase exhibited excellent 2S,3R-enantioselectivity against 2-methyl-3-(para-substituted-phenyl)oxiranecarboxamides. Under very mild conditions, biotransformations of nitriles provided an efficient and practical synthesis of 2R,3S-(-)-3-aryl-2-methyloxiranecarboxamides, electrophilic epoxides with tertiary and quaternary stereocenters, in excellent yield with enantiomeric excess greater than 99.5%. The synthetic applications of the resulting enantiomerically pure epoxides were demonstrated by convenient and straightforward syntheses of polyfunctionalized chiral molecules possessing a quaternary stereocenter such as R-(+)-2-hydroxy-2-methyl-3-phenylpropionic acid, 2R,3R-(-)-3-amino-2-hydroxy-2-methyl-3-phenylpropionic acid, and 2S,3S-(+)-2-amino-3-hydroxy-2-methyl-3-phenylpropionic acid, employing the regio- and stereospecific epoxide ring opening reactions of 2R,3S-(-)-2-methyl-3-phenyloxiranecarboxamide as the key steps.     

(1R,3S,4S)-2-苄氧羰基-2-氮杂双环[2.2.1]庚烷-3-羧酸的合成

以(R)-(+)-α-甲基苄胺为原料,依次经缩合,Diels-Alder反应,还原,Cbz-保护和水解反应,合成了抗丙肝新药HCV NS3/4A蛋白酶拟肽类抑制剂的重要中间体——(1R,3S,4S)-2-苄氧羰基-2-氮杂双环[2.2.1]庚烷-3-羧酸,总收率66%,其结构经1H NMR和ESI-MS确证。