Total synthesis of (+) methyl β-d-vicenisaminide

The total synthesis of methyl β-d-vicenisaminide 1 has been achieved. In this approach, the synthesis of enantiomerically pure methyl (4R,5S)- and (4S,5R)-4-azido-5-hydroxy-2(E)-hexenoates 2 was established by enzymatic resolution of (±)-anti-5-acetoxy -4-azido-2(E)-hexenoate 4. Another stereogenic center was introduced by base-catalyzed intramolecular conjugate addition of a hemiacetal-derived alkoxide nucleophile obtained by the reaction of methyl (4S,5R)-N-4-tert-butoxycarbonyl-N-methylamino-5-hydroxyl-2(E)-hexenoate 8 and benzaldehyde in the presence of a base.     

Chemoenzymatic synthesis of (3S,4S)- and (3R,4R)-3-methoxy-4-methylaminopyrrolidine

Facile chemoenzymatic enantioselective synthesis of (3S,4S)-3-methoxy-4-methylaminopyrrolidine, a key intermediate for a new quinolone antitumor compound AG-7352 has been described. This methodology illustrates the preparation of 3-azido-1-benzyloxycarbonyl-4-hydroxypyrrolidine starting from diallylamine via 1-benzyloxycarbonyl-3-pyrroline obtained by ring-closing metathesis (RCM) employing Grubbs’ catalyst. Enzymatic transesterification employing PS-C lipase gave (3S,4S)-3-azido-1-benzyloxycarbonyl-4-hydroxypyrrolidine in >99% ee, which upon methylation of the hydroxyl group followed by sequential reactions gave the desired intermediates, (3S,4S)-1-tert-butoxycarbonyl-3-tert-butoxycarbonylamino-4-methoxypyrrolidine.     

Five-membered 2,3-dioxo heterocycles: CVI. Acylation of substituted (Z)-2-[1,3,4,4a,5,10b-Hexahydrophenanthridin-6(2H)-ylidene]acetamide with aroylketenes. crystal and molecular structure of substituted N-{(Z)-2-[1,3,4,4a,5,10b-Hexahydrophenanthridin-6(2H)-ylidene]acetyl}acrylamide

Aroylketenes generated by thermolysis of 6-aryl-2,2-dimethyl-4H-1,3-dioxin-4-ones reacted with (Z)-2-[4a,7,10-trimethyl-1,3,4,4a,5,10b-hexahydrophenanthridin-6(2H)-ylidene]acetamide to give (Z)-3-aryl-3-hydroxy-N-{(Z)-2-[4a,7,10-trimethyl-1,3,4,4a,5,10b-hexahydrophenanthridin-6(2H)-ylidene]acetyl}acrylamides whose structure was confirmed by X-ray analysis.     

Chemoenzymatic synthesis of (3R,4S)- and (3S,4R)-3-methoxy-4-methylaminopyrrolidine

An efficient and a convenient enantioselective synthesis of (3R,4S)-3-methoxy-4-methylaminopyrrolidine has been carried out by a lipase-mediated resolution protocol. This method describes the preparation of (±)-1-Cbz-cis-3-azido-4-hydroxypyrrolidine starting from commercially available diallylamine followed by ring-closing metathesis (RCM) via S_N2 displacement reactions. Pseudomonas cepacia lipase immobilized on diatomaceous earth (Amano PS-D) provides (3R,4S)-11 and (3S,4R)-12 in an excellent enantiomeric excess.     

2-Amino-4-(aminomethyl)thiazole-based derivatives as potential antitumor agents: design,synthesis, cytotoxicity and apoptosis inducing activities

Novel 2-amino-4-(aminomethyl)thiazole derivatives were designed and synthesized by a facile method including the Hantzsch construction of thiazole core followed by amidation and nucleophilic substitution steps. Bioassay results showed that 4-(tert-butyl)-N-[4-(piperazin-1-ylmethyl)thiazol-2-yl]-benzamide and 4-(tert-butyl)-N-{4-[(4-piperidinopiperidin-1-yl)methyl]thiazol-2-yl}benzamide possessed similar activities compared with 5-fluorouracil. The 4-piperidino-piperidin-1-yl-containing derivative also suppressed proliferation of cultured tumor cells by inducing apoptosis.     

Preparation of (2E,4E)-2-(2-benzyloxyethyl)-5-(3-methoxy-4-chlorophenyl)penta-2,4-dienal as a key intermediate in the synthesis of strobilurin B

(2E,4E)-2-(2-Benzyloxyethyl)-5-(4-chloro-3-methoxyphenyl)penta-2,4-dienal was obtained by the condensation of 4-benzyloxybutanal N-tert-butylimine with 4-chloro-3-methoxycinnamic aldehyde with ≥98% configurational purity and 40% yield. When 4-benzyloxy-2-triethylsilylbutanal imine was used, a 7: 3 mixture of the target (2E,4E)-dienal with its (2Z,4E)-isomer was obtained in 60% yield; the latter quantitatively isomerized to the thermodynamically preferable target (2E,4E)-dienal.     

Biocatalytic reduction system for the production of chiral methyl (R)/(S)-4-bromo-3-hydroxybutyrate

An effective method for producing methyl 4-bromo-3-hydroxybutyrate enantiomers was developed using an engineered protein. Escherichia coli transformant cells containing a mutant β-keto ester reductase (KER-L54Q) from Penicillium citrinum and a cofactor-regeneration enzyme such as glucose dehydrogenase (GDH) or Leifsonia sp. alcohol dehydrogenase (LSADH) were used to produce methyl (S)-4-bromo-3-hydroxybutyrate from methyl 4-bromo-3-oxobutyrate. On the other hand, the production of methyl (R)-4-bromo-3-hydroxybutyrate was achieved by asymmetric reduction of methyl 4-bromo-3-oxobutyrate with a mutant phenylacetaldehyde reductase (PAR-HAR1) from Rhodococcus sp. ST-10.     

Synthesis of 4-(2-hydroxyaryl)-3-nitro-4H-chromenes

A combinatorial library of 4-(2-hydroxyaryl)-3-nitro-4H-chromenes was synthesized in high yield by C4-SMe substitution in N-alkyl/phenyl 4-(methylthio)-3-nitro-4H-chromen-2-amines with a variety of phenols. The reaction always provided C2 substitution in the phenol ring, dictated by hydrogen bond interactions between the phenolic hydroxyl group and the nitro group in 3-nitro-4H-chromenes. Reduction of the nitro group with concomitant hydrolysis of the enamine in 4-(2-hydroxyaryl)-3-nitro-4H-chromenes with Zn, Ac₂O in AcOH furnished hybrid amino-acid lactone incorporating ortho-tyrosine and phenyl alanine moieties.     

Stereoselective enzymatic synthesis of monoglucosyl-myo-inositols with in vivo anti-inflammatory activity

The monoglucosyl-inositols α-d-glucopyranosyl-(1→4)-4d-myo-inositol 3 and α-d-glucopyranosyl-(1→1)-1d-myo-inositol 4 were synthesized by a combined enzymatic transglucosylation and hydrolysis strategy, using cyclodextrin glucosyl transferase (CGTase) from Thermoanaerobacter sp., followed by hydrolysis with Aspergillus niger glucoamylase. The glucosides were separated by preparative HPLC and fully characterized by extensive 1D and 2D NMR studies. The structure of the regioisomer 4 was confirmed by X-ray crystallography of its perbenzoylated derivative 4a. Both isomers demonstrated in vivo anti-inflammatory activity at comparative levels to corticosterone on mouse ear oedema induced by 12-O-tetradecanoylphorbol-13-acetate (TPA) and in rat hind paw oedema induced by carrageenan.     

Precursors to oak lactone. Part 2: Synthesis, separation and cleavage of several β-d-glucopyranosides of 3-methyl-4-hydroxyoctanoic acid

The β-d-glucopyranosides of all four stereoisomers of 3-methyl-4-hydroxyoctanoic acid have been prepared. The (3S,4S) and (3R,4R) species were prepared from cis-5-n-butyl-4-methyl-4,5-dihydro-2(3H)-furanone (cis-oak lactone) by a process involving ring-opening with base and protection of the carboxyl function as its benzyl ester. The glucose unit was introduced by a modified Koenigs-Knorr procedure. A different strategy was necessary for synthesis of the (3S,4R) and (3R,4S) compounds. This was based on the reductive ring-opening of trans-oak lactone and subsequent protection of the primary alcohol as its t-butyldiphenylsilyl ether. Separation of the individual glucosides was effected by preparative thin layer chromatography. Those corresponding to the nature-identical isomers of oak lactone have been shown to produce oak lactone under both acidic hydrolysis and pyrolysis conditions. The galloyl-β-d-glucoside of the cis-species, obtained as a natural isolate from the wood of Platycarya strobilacea, was also found to produce cis-oak lactone upon both acid hydrolysis and pyrolysis. Both the nature-identical (4S,5S) cis-oak lactone and its non-natural (4R,5R) enantiomer have been prepared from their corresponding glycosides and their aroma thresholds in white wine were determined to be 23 and 82 μg/L (ppb) respectively. The aroma threshold of the nature-identical isomer in a red wine was 46 μg/L.     

The crystal structure and phase transitions of LiBaPO4

Polymorphism in lithium barium phosphate (LiBaPO₄) was investigated by synchrotron X-ray diffraction (sXRD) and high temperature X-ray diffraction (HT-XRD). Two modifications were isolated using different cooling rates from the synthesis temperature to room temperature. The slowly-cooled sample exhibited a monoclinic structure with a Cc space group (denoted as M-LiBaPO₄) while the quenched sample belonged to a trigonal system with a P31c space group (denoted as T-LiBaPO₄). In both structures, LiO₄ and PO₄ tetrahedra are linked alternatively by sharing each corner in the lattice, forming tridymite-type six-membered rings. The voids in the anionic framework are filled by Ba atoms. The monoclinic distortion in M-LiBaPO₄ can be attributed to “polyhedral tilting” which shifts the axial bridging oxygens from the centroid of the PO₄ tetrahedron, breaking the three-fold symmetry in the trigonal structure. The HT-XRD data upon heating from 298 to 1373 K indicate successive structural transitions as follows; M-LiBaPO₄ (Cc) → T-LiBaPO₄ (P31c) → H-LiBaPO₄ (P6₃) → O-LiBaPO₄ (Pmcn). H-LiBaPO₄ and O-LiBaPO₄ denote the phases exhibiting the hexagonal and orthorhombic systems, respectively. The thermal evolution of the crystal structure of LiBaPO₄ is quite similar to that of LiKSO₄. The sequences of space group change in both compounds are nearly identical and only the transition temperatures differ.     

Absolute configuration of (−)-4-methylheptan-3-ol,a pheromone of the smaller european elm bark beetle,as determined by the synthesis of its (3R,4R)-(+)- and (3S,4R)-(+)-isomers

Nerol and geraniol were stereoselectively converted to (±)-threo- and (±)-erythro-4-methylheptan-3-ol respectively. (R)-(+)-Citronellic acid was converted to a mixture of (3R,4R)-(+)-threo- and (3S,4R)-(+)-erythro-isomers which was separable by GLC. These syntheses established the absolute configuration of the naturally occurring (?)-4-methylheptan-3-ol to be 3S,4S.     

π-Extended conjugate phenylacetylenes. Synthesis of 4-[(E) and (Z)-2-(4-ethenylphenyl)ethenyl]pyridine. Dimerization, quaternation and formation of charge-transfer complexes

The conjugate (E)- and (Z)-(4′-pyridylethenyl)-4-phenylethyne (E-4 and Z-4) has been satisfactorily prepared by two different routes: (a) by dehydrohalogenation of 4′-pyridylethenyl-4-phenyl-β-chloroethene; (b) by the Wittig reaction between p-(iodobenzyl)(triphenyl)phosphine ylide and 4-pyridinecarboxaldehyde, E/Z isomer separation, and cross-coupling with 2-methyl-but-3-yn-2-ol followed the propanone elimination. The Glaser oxidative dimerization of (Z)-4 yields (Z,Z)-1,4-di[(4′-pyridylethenyl)-4-phenyl]-buta-1,3-diyne in good yield, (Z,Z)-5. (E,E)-5 was obtained by phase transfer oxidative dimerisation of (E)-4 in presence of their N-methyl salt (E)-10. Mono- and di-N-methylated salts of conjugate (E,E)-5 and (Z,Z)-5, were obtained by quaternation with iodomethane. The (Z,Z)-5 di-N-methylated salt forms charge-transfer complexes with TCNE, TCNQ and TMPD.     

A new approach to the synthesis of ethyl (4E)-alkenoates

A new approach to the preparation of ethyl (4E)-alkenoates was developed on the basis of Fe-catalyzed cross-coupling of ethyl (4E)-5-chloropent-4-enoate with the Grignard reagents. The starting ethyl (4E)-5-chloropent-4-enoate was obtained by alkylation of malonic ester of (E)-1,3-dichloropropene followed by decarbethoxylation.     

Metalloporphyrins as chemical shift reagents: the unambiguous NMR characterization of the cis- and trans-isomers of meso-(bis)-4′-pyridyl-(bis)-4′-carboxymethylphenylporphyrins

The condensation of pyrrole with 4-pyridylcarboxyaldehyde and methyl 4-formyl benzoate under Adler-Longo conditions yielded the series of meso-(4′-pyridyl)/(4′-carboxymethylphenyl)porphyrins as a mixture. Careful column chromatography afforded each isomer in pure form. In this paper we focus on the two bis-substituted isomeric meso-porphyrins, 5,10-bis(4′-pyridyl)-15,20-bis(4′-carboxymethylphenyl)porphyrin and 5,15-bis(4′-pyridyl)-10,20-bis(4′-carboxymethylphenyl)porphyrin, respectively, 4′-cis and 4′-transDPyDMeP. The assignment of the geometry of the two isomers was performed by ¹H NMR spectroscopy on the trinuclear adducts [(4′-cisDPyDMeP){Ru(TPP)(CO)}₂] and [(4′-transDPyDMeP){Ru(TPP)(CO)}₂], obtained by selective coordination of [Ru(TPP)(CO)(EtOH)] (TPP=tetraphenylporphyrin) to the peripheral nitrogen atoms. The axially bound ruthenium porphyrins act as chemical shift reagents on the central porphyrin, allowing a clear distinction of the pyrrole proton resonances and consequent unambiguous assignment of the geometry of each isomer based upon symmetry considerations.     

Synthesis and spectroscopic characterization of enantiopure protected trans-4-amino-1-oxyl-2,2,6,6-tetramethyl piperidine-3-carboxylic acid (trans β-TOAC)

Enantiomerically pure (3R,4S) and (3S,4R) protected 4-amino-1-oxyl-2,2,6,6-tetramethylpiperidine-3-carboxylic acids were synthesized by reduction of the enamines resulting from the condensation of 3-carboxymethyl-1-oxyl-2,2,6,6-tetramethyl-4-piperidone with (R) or (S)-α-methylbenzylamine. While NaBH₃CN/CH₃COOH reduction gave predominantly a mixture of the two possible cis-diastereomers, the use of NaBH₄/(CH₃)₂CHCOOH resulted in a mixture of only one trans- and one cis-diastereomer. Removal of the chiral auxiliary from the separated diastereoisomers by hydrogenolysis and regeneration of the nitroxide radical gave the desired β-amino esters. The ESR spectrum of the (3R,4S)-enantiomer is also reported.     

(R)-4-Hydroxymethyl-2-phenyl-4,5-dihydrooxazol-4-ylmethyl acetate: chiral building block for the synthesis of optically active α-substituted α-amino acid derivatives

(R)-4-Hydroxymethyl-2-phenyl-4,5-dihydrooxazol-4-ylmethyl acetate was efficiently obtained by lipase-catalyzed asymmetrization of the prochiral diol. (R)-4-Hydroxymethyl-2-phenyl-4,5-dihydrooxazol-4-ylmethyl acetate was converted to (R)-2-(hydroxymethyl)glutamic acid and a synthetic intermediate of (−)-deoxydysibetaine.     

Divergent and solvent dependent reactions of 4-ethoxycarbonyl-3-methyl-1-tert-butoxycarbonyl-1,2-diaza-1,3-diene with enamines

Starting from 1-tert-butyloxycarbonyl-3-methyl-4-ethoxycarbonyl-1,2-diaza-1,3-diene and β,β,β and α,β-substituted enamines a careful choice of solvents and temperatures allows the divergent synthesis of 5,6-dihydro-4H-pyridazines, 2-(1-N-boc-hydrazono-ethyl)-4-pyrrolidin-1-yl-but-3-enoic acid ethyl ester, and 1-amino-pyrroles. Moreover, some interesting conclusions about the mechanism(s) of the reaction have been drawn by careful analysis of products' structure and distribution. Thus, the reaction may proceed through a stereospecific [4+2] cycloaddition mechanism giving rise to 5,6-dihydro-4H-pyridazines or by simple addition or domino addition/cyclization pathways affording, respectively, 2-(1-N-boc-hydrazono-ethyl)-4-pyrrolidin-1-yl-but-3-enoic acid ethyl ester and 1-amino-pyrroles (formally the [3+2] cycloaddition product).     

Synthesis, structures and magnetic properties of the new vanadates AgMnVO4 and RbMnVO4

The new compounds, AgMnVO₄ and RbMnVO₄ have been synthesized by solid state reaction route. Their crystal structures were determined from single-crystal X-ray diffraction data for RbMnVO₄ and powder X-ray diffraction data for AgMnVO₄. AgMnVO₄ crystallizes with the maricite-type structure in space group Pnma, a=9.5778(6) Å, b=6.8518(4) Å, c=5.3734(3) Å and Z=4. RbMnVO₄ crystallizes in space group P6₃ with a stuffed tridymite-type structure, a=11.2584(3), c=8.9893(13) Å and Z=8. A merohedral twinning was taken into account for its structural refinement. To our knowledge this is the first vanadate showing this structural type. AgMnVO₄ and RbMnVO₄ were characterized by magnetic susceptibility and specific heat measurements. AgMnVO₄ is antiferromagnetic with a Néel temperature of 12.3 K determined by specific heat measurements. RbMnVO₄ exhibits canted antiferromagnetism with a Néel temperature of 6.5 K.     

A chemoselective hydroxymethylation: new route for the synthesis of 6-aroyl-4-(4H-triazol-3-yl)thiomorpholin-3-ones

Treatment of 2-(2-oxo-2-arylethylthio)-N-(4H-1,2,4-triazol-3-yl)acetamides with paraformaldehyde in the presence of a base has led to a tandem chemoselective hydroxymethylation followed by cyclization yielding a set of novel 6-aroyl-4-(4H-triazol-3-yl)thiomorpholin-3-ones. The thiomorpholine ring has been found to have a boat like conformation in these compounds as evidenced by NOESY NMR spectrum.