Direct epoxidation of D-glucal and D-galactal derivatives with in situ generated DMDO

A multi-gram epoxidation of 3,4,6-tri-O-benzyl-D-glucal and D-galactal with dimethyldioxirane (DMDO) generated in situ from Oxone/acetone in a biphasic system (CH(2)Cl(2)-aqueous NaHCO(3)) resulted in the formation of the corresponding 1,2-anhydrosugars in a 99% yield and 100% selectivity. In a similar way, 3,4,6-tri-O-acetyl-D-glucal afforded a 7:1 mixture of the corresponding gluco and manno derivatives in an 87% overall yield.     

Cyclic peptides. XXVI. Synthesis of AM-toxin II analogs by cyclization through ester bond formation

In order to explore the route for the preparation of cyclodepsipeptide by cyclization through an ester bond formation, two analogs of AM-toxin II, cyclotetradepsipeptide, were synthesized. As a preliminary experiment, synthesis of [L-Phe3, L-Ser(Bzl)4]-AM-toxin II, containing L-Phe and L-Ser(Bzl) in place of L-App (2-amino-5-phenyl-pentanoic acid) and delta Ala (alpha, beta-dehydroalanine), respectively, was attempted. Cyclization of H-L-Hmb-L-Phe-L-Ser(Bzl)-L-Ala-OH in CH2Cl2 at 10 mM concentration using water-soluble carbodiimide (EDC) and 4-dimethylaminopyridine (DMAP) successfully gave a cyclic monomer in 16% yield. Cyclization of H-L-Hmb-L-App-L-Ser(Bzl)-L-Ala-OH under the same conditions also afforded a cyclic monomer, [L-Ser(Bzl)4]AM-toxin II, in 19% yield. Analytical parameters of these cyclic monomers obtained were identical to those of the authentic samples obtained by cyclization through a peptide bond formation.     

Preparation of dopaminergic N-alkyl-benzyltetrahydroisoquinolines using a 'one-pot' procedure in acid medium

The preparation of N-methyl-BTHIQ (4) from N-phenylethyl-phenacetamide (1) by cyclization, reduction and N-alkylation in acid medium has been achieved in good yield in a 'one-pot' procedure. Acylation of imine (2) intermediate afforded the Z and E stereoselectivity in the enamide formation. 6-Hydroxy-BTHIQ (7) shows selectivity for D2 dopamine receptors, while its N-methylated homologue (8) displays higher affinities for both D1 and D2 receptor types, with an unexpected increase in D1 dopamine receptor affinity.     

Chemoenzymatic synthesis of (E)-3,7-dimethyl-2-octene-1,8-diol isolated from the hairpencils of male Danaus chrysippus (African Monarch)

The synthesis of (E)-3,7-dimethyl-2-octene-1,8-diol (1), which was isolated from the hairpencils of male Danaus chrysippus (African Monarch), was investigated. The key step of the sequence involves asymmetric desymmetrization of the 1,3-propanediol 7 with lipase, in which high enantioselectivity was observed. Total synthesis afforded (S)-1 in 12 steps and 26% overall yield from readily available geraniol.     

Lanostanes and friedolanostanes from the pericarp of Garcinia hombroniana

The CH2Cl2 extract from the pericarp of Garcinia hombroniana yielded three 17,14-friedolanostanes [(24E)-3alpha-hydroxy-17,14-friedolanostan-8, 14,24-trien-26-oic acid, methyl (24E)-3alpha,23-dihydroxy-17,14-friedolanostan-8,14,24 -trien-26-oate and methyl (24E)-3alpha,9,23-trihydroxy-17,14-friedolanostan-14,2 4-dien-26-oate] and two lanostanes [3beta- and 3alpha-hydroxy-23-oxo-9,16-lanostadien-26-oic acid]. The structure of (14E)-3alpha-hydroxy-17,14-friedolanostan-8,14,24-trie n-26-oic acid was determined using spectroscopic and X-ray analyses, while the structures of the other compounds were elucidated solely from analysis of spectroscopic data.     

Glucosylation of phenols and phenylalkyl alcohols using cultured plant cells

Cultured plant cells of Eucalyptus perriniana can convert phenol and phenylalkyl alcohols [C(6)H(5)(CH(2))(n)OH, n=0-3] into the corresponding beta-D-glucopyranosides in a good yield. The cells preferentially glucosylated phenylmethanol (n=1, 59% yield) rather than phenol (n=0, 49%), 2-phenylethanol (n=2, 38%), and 3-phenylpropan-1-ol (n=3, 20%). On the other hand, 2-, 3-, and 4-hydroxyphenylmethanols were also glucosylated to (hydroxymethyl)phenyl beta-D-glucopyranosides and (hydroxyphenyl)methyl beta-D-glucopyranosides by cultured E. perriniana cells.     

A new high-yield synthetic route to PET CB1 radioligands [11C]OMAR and its analogs

OMAR analogs reference standards and their corresponding desmethylated precursors were synthesized from substituted anilines either in 4 and 5 steps with 27-32% and 24-31% yield, or in 3 and 4 steps with 21-30% and 19-28% yield, respectively. [(11)C]OMAR and its analog radioligands were prepared from their desmethylated precursors with [(11)C]CH(3)OTf through O-[(11)C]methylation and isolated by HPLC combined with solid-phase extraction (SPE) in 50-65% radiochemical yields based on [(11)C]CO(2) and decay corrected to end of bombardment (EOB), with 370-740 GBq/μmol specific activity at EOB.     

Reductive formation of carbon monoxide from CCl4 and FREONs 11, 12, and 13 catalyzed by corrinoids

In an earlier publication, we reported that corrinoids catalyze the sequential reduction of CCl4 to CHCl3, CH2Cl2, CH3Cl, and CH4 with titanium(III) citrate as electron donor [Krone, U. E., Thauer, R. K., & Hogenkamp, H. P. C. (1989) Biochemistry 28, 4908-4914]. However, the recovery of these products was less than 50%, indicating that other products were formed. We now report that, under the same experimental conditions, CCl4 is also converted to carbon monoxide. These studies were extended to include FREONs 11, 12, 13, and 14. Corrinoids were found to catalyze the reduction of CFCl3, CF2Cl2, and CF3Cl to CO and, in the case of CFCl3, to a lesser extent, to formate. CF4 was not reduced. The rate of CO and formate formation paralleled that of fluoride release. Both rates decreased in the series CFCl3, CF2Cl2, CCl4, and CF3Cl. The reduction of CFCl3 gave, in addition to CO and formate, CHFCl2, CH2FCl, CH3F, C2F2Cl2, and C2F2Cl4. The product pattern indicates that the corrinoid-mediated reduction of halogenated C1-hydrocarbons involves the intermediacy of dihalocarbenes, which may be a reason why these compounds are highly toxic for anaerobic bacteria.     

Conformationally constrained ethylenediamines: synthesis and receptor binding of 6,8-diazabicyclo[3.2.2]nonanes

The synthesis and receptor affinity of 6,8-diazabicyclo[3.2.2]nonanes representing conformationally constrained ethylenediamines are described. The Dieckmann analogous cyclization of the (piperazin-2-yl)propionate 9 provided the bicyclononane 10 only, when the first cyclization product was trapped with chlorotrimethylsilane. 10 was stereoselectively transformed into the bicyclic amines 19a,b and amides 22a,b, which were investigated in competition experiments with radioligands for their sigma(1)-, sigma(2)-, kappa-, and mu-receptor affinities. The (2R)-configured dimethylamine 19a showed promising sigma(1)-receptor affinity (K(i)=23.8 nM) and selectivity, whereas the (2S)-configured (dichlorophenyl)acetamide 22b displayed a sigma-receptor binding profile (sigma(1): K(i)=184 nM; sigma(2): K(i)=263 nM) very similar to the binding profile of the atypical antipsychotic BMY-14802 (26).     

Solid-supported and pegylated H-Pro-Pro-Asp-NHR as catalysts for asymmetric aldol reactions

H-Pro-Pro-Asp-NH2 is a highly active and selective catalyst for asymmetric aldol reactions. Here, the versatility of H-Pro-Pro-Asp-NH2 has been further improved by immobilization on a solid support and functionalization with a short polyethylene glycol linker at the C-terminus. The development, synthesis, and the catalytic properties in aldol reactions of H-Pro-Pro-Asp-resin and H-Pro-Pro-Asp-Ahx-NH(CH2CH2O)3CH3 are described. For the solid-supported catalyst, TentaGel with a loading of 0.1-0.2 mmol g(-1) proved to be the optimal support. The solid-supported catalyst can be recycled at least three times without a significant drop in the catalytic activity or selectivity. Using the pegylated catalyst H-Pro-Pro-Asp-Ahx-NH(CH2CH2O)3CH3, only 0.5 mol % are necessary to obtain aldol products in up to 96% yield and 91% enantiomeric excess. In all cases, enantioselectivities are comparable to those obtained with the parent catalyst H-Pro-Pro-Asp-NH2. Thus, immobilization of H-Pro-Pro-Asp-NH2 on Tentagel as well as pegylation led to catalysts with selectivities comparable to the nonmodified catalyst, exhibiting additional distinct advantages such as facile reusability, ease of handling, higher solubility, and thereby greater versatility. handling, higher solubility, and thereby greater versatility.     

Towards alpha- or beta-D-C-glycosyl compounds by tin-catalyzed addition of glycosyl radicals to acrylonitrile and vinylphosphonate,and flexible reduction of tetra-O-acetyl-alpha-D-glucopyranosyl bromide with cyanoborohydride

Photo-induced radical addition of acetylated alpha-D-glucopyranosyl bromide (1). to acrylonitrile or diethyl vinylphosphonate, in the presence of catalytic amounts of tri-n-butyltin chloride and sodium (or tetra-n-butylammonium) cyanoborohydride in excess, allowed efficient preparations of alpha-configurated nonononitrile and 2-(alpha-D-glucopyranosyl)-ethylphosphonate (79, 70% yields, respectively). These conditions led to 2-(alpha-D-manno-, and galactopyranosyl)-ethylphosphonates in 68 and 76% yields. Similarly, radical addition of acetylated 1-bromo-beta-D-glucopyranosyl chloride (2). to acrylonitrile or diethyl vinylphosphonate afforded mainly intermediate chlorides which, upon radical reduction with excess tri-n-butyltin hydride, afforded the corresponding beta anomers (40 and 38%, respectively) by sequential C-C and C-H bond formation. Stereocontrol relies on the alpha-stereoselective quenching of D-glycopyranos-1-yl radicals. We found also that UV light irradiation of 1 with excess NaBH(3)CN in tert-butanol afforded either 1,3,4,6-tetra-O-acetyl-2-deoxy-alpha-D-arabino-hexopyranose (65% after crystallization) or, when 10% mol thiophenol was added, 2,3,4,6-tetra-O-acetyl-1,5-anhydro-D-glucitol (79%). These are simple, tin-free, and easily controlled conditions, which compare well with known preparations of these reduced sugars.     

N-terminal amino acid sequence analyses of the alpha and beta polypeptides from four distinct subsets of sheep major histocompatibility complex class II molecules

Four monoclonal antibodies, SBU.II 28-1, 37-68, 38-27, and 42-20, each recognizing a distinct, non-overlapping subset of sheep class II molecules, were used to purify class II molecules from a single sheep. Four class II alpha subunits designated 28-1 alpha, 37-68 alpha, 42-20 alpha, and 38-27 alpha and five class II beta subunits designated 28-1 beta, 37-68 beta 1, 37-68 beta 2, 42-20 beta, and 38-27 beta were compared by N-terminal sequence analyses. Two distinct alpha subunits were identified; the 28-1 alpha, 37-68 alpha, and 42-20 alpha subunits all had identical N-terminal amino acids sequences, which exhibited about 75% homology with HLA-DR alpha and mouse E alpha polypeptides. In contrast, the 38-27 alpha sequence exhibited about 80% sequence homology with HLA-DQ alpha and mouse A alpha polypeptides. In general, sheep beta subunits displayed insufficient sequence homology to enable correlation with human beta-chain sequences; however, the 38-27 beta-chain sequence showed homology with the HLA-DQ beta sequence. The conserved sequence surrounding the site for N-linked glycosylation within human/mouse beta polypeptides (residues 19 to 21) was not present in sheep beta sequences and in contrast with the beta-chains of mouse and man, sheep beta polypeptides contained between 1 and 3 positionally variable cysteine residues (residues 13 to 15 inclusive). Individual sheep beta subunits exhibited extensive sequence heterogeneity and each consisted of a unique population of beta polypeptide species. At least 16 different beta polypeptide sequences were identified from a single sheep and the existence of no fewer than nine non-allelic beta genes was inferred from the sequence data. We have previously provided evidence suggesting that the sheep has multiple major histocompatibility complex class II alpha and beta genes related to those of all three HLA-D subregions. The present results suggest that a number of these genes encode HLA-DQ-like heterodimers and that a sheep DR-like alpha gene product is shared with the products of a large and heterogeneous sheep beta gene family.     

A convenient synthesis of 2'-deoxy-2-fluoroadenosine; a potential prodrug for suicide gene therapy

A convenient synthesis of 2'-deoxy-2-fluoro-adenosine (1) is described. Deaminative fluorination of 2-aminoadenosine (2) followed by silylation of the 3', 5'-hydroxyl groups gave the corresponding 2-fluoroadenosine derivative 4 in good yield. Thiocarbonylation of 4 to thiocarbonylimidazolyl derivative 5a followed by treatment with an excess of tris(trimethylsilyl)silane (TTMSS) and tert-butyl peroxide in toluene at 80 degrees C was found to affect an efficient deoxygenation to the corresponding 2'-deoxy derivative 6. Desilylation of 6 by Et4NF in CH3CN afforded 1 in high yield.     

An efficient process for the synthesis of cyclic HPMPC

1-[((S)-2-Hydroxy-2-oxo-1,4,2-dioxaphosphorinan-5-yl)methyl] cytosine (cyclic HPMPC) was readily synthesized in gram to multi-kilogram quantities by treating a DMF suspension of HPMPC with four molar equivalents of ethyl chloroformate. This dehydrative intramolecular cyclization process typically afforded cHPMPC in 94% isolated yield and high purity. Benign by-products and solvents were easily removed.     

The fractionation of chlorine isotopes by the aerobic methylotrophic bacterium Methylobacterium dichloromethanicum grown on dichloromethane

Methylobacterium dichloromethanicum was found to be able to utilize dichloromethane (DCM) as the source of carbon and energy with the production of biomass, CO2, and HCl. A comparative analysis of abundances of the major DCM isotopomers 35Cl(2)12C1H2, 35Cl37Cl12C1H2 and 37Cl(2)12CH2 made it possible to estimate the fractionation of chlorine isotopes during the bacterial metabolism of DCM. The kinetic chlorine isotope effects for 35Cl37Cl12C1H2 (m/z 86) and 37Cl(2)12C1H2 (m/z 88) relative to 35Cl(2)12C1H2 (m/z 84) turned out to be alpha 86/84 = 1.006 +/- 0.002 and alpha 88/84 = 1.023 +/- 0.003, respectively. The inference is made that the growth of M. dichloromethanicum on DCM is accompanied by the mass-independent fractionation of the DCM isotopomers.     

High yield synthesis of tentoxin, a cyclic tetrapeptide.

Tentoxin is a naturally occurring phytotoxic cyclic tetrapeptide excreted by fungi of the Alternaria alternata family. The four total syntheses of tentoxin published to date give poor total yields, mainly owing to two difficulties, the introduction of the dehydro amino acid and more especially the cyclization step. Here we describe a method that stereospecifically introduces Z-dehydrophenylalanine (deltaZPhe) by a modified Erlenmeyer aldolization reaction. The linear tetrapeptide, Boc-R1Ala-Leu-R2deltaZPhe-G1y-OMe (R1, R2: CH3, 14CH3), the precursor of tentoxin, was obtained in a 72% yield from Boc-Leu-Gly-OH. This linear tetrapeptide, labelled with carbon-14, was used for a comparative study of four cyclization reagents DPPA, DCC-PfpOH, HBTU and HATU. This last was the most effective and gave tentoxin in a 81% cyclization yield. The activated ester formed with this reagent displayed an enhanced capacity for cyclization, permitting cyclization in concentrated medium (10 mM). This new synthetic route gave tentoxin in a 60% yield from Boc-Leu-Gly-OH and offers a means of achieving the synthesis of hitherto elusive analogues.     

Cryopreservation of Echinococcus multilocularis metacestodes and subsequent proliferation in rodents (Meriones)

Four isolates of larval Echinococcus multilocularis originating from Switzerland (CH/1, CH/6 and CH/22) and Alaska (A/1) were used to prepare crude homogenate or small tissue fragments (STF) in Eagle's Minimal Essential Medium with Earle's salts (EMEM/A), or 0.2 g tissue blocks (TB) which were suspended in the same medium. After addition of dimethylsulfoxide or glycerol in final concentrations of 5% and 10% (v/v), respectively, aliquots of 1.0 ml, containing either 0.1 ml crude homogenate or STF, or one block of 0.2 g, were kept in cryotubes for 30 min at +2-4 degrees C (precooling phase), cooled subsequently to lower temperatures following a two-step or three-step schedule and finally plunged into liquid nitrogen (-196 degrees C). After storage for one week the samples were rapidly thawed at +37 degrees C for approximately 3 min, washed in fresh EMEM/A (37 degrees C) and transferred into the peritoneal cavity of Meriones for viability testing. As judged by histological examinations and metacestode weights of each 24 Meriones infected with cryopreserved homogenate, STF or TB, respectively, 46%, 87% or 100% contained viable, proliferating parasites. The best proliferation rate occurred when 10% glycerol was used as cryoprotectant and after precooling a three-step freezing schedule was employed (30 min at -28 degrees C, 30 min at -80 degrees C, transfer to liquid nitrogen). Cooling rates were determined as 0.7, 1.0 and 1.7 degrees C min-1 for the precooling phase, step 1 and step 2, respectively, and estimated as 65 degrees C min-1 for step 3. These results demonstrate that metacestodes of E. multilocularis can be successfully maintained by cryopreservation without losing their proliferative capacity in the intermediate host.     

Germacranolides from Artemisia myriantha and their conformation

The CH(2)Cl(2) extract of the aerial parts of Artemisia myriantha afforded three germacranolides derived from 13-acetoxy-3beta-hydroxy-germacra-1(10)E,4E,7(11)-trien-12,6alpha-olide, whose structures were elucidated by 2D-NMR spectroscopic analyses. Some conclusions are drawn about the possible conformations of the ten-membered germacranolide ring system from the exchange peaks seen in the NOESY spectra, and an estimate is made of the energy barrier to ring-flipping from variable-temperature NOESY experiments. The conclusions reached were supported by molecular modeling studies and an NMR spectroscopic investigation of the commercially available germacranolide, parthenolide.     

Acyl migration on nucleic acid compounds related to adenosine

Treatment of N6,N6-di-p-toluyl-2',3'-O-isopropylideneadenosine (7) with ZnBr2 in 1,4-dioxane afforded a 8,5'-O-cycloadenosine derivative 8 exclusively. Reaction of 2',3'-O-isopropylideneadenosine (1) with p-cyanobenzoyl chloride in a CH2Cl2-Et3N mixture afforded a ring-cleaved compound 11 as the main product.