Isolation of iso-grayanotoxin II from leaves of Leucothoe grayana Max. Its X-ray crystallographic analysis and acute toxicity in mice

The structure of iso-grayanotoxin II, a new diterpenoid from Leucothoe grayana MAX., has been determined as 3 beta,5 beta,6 beta,14 beta,16 alpha-pentahydroxygrayanotox-9(10)-ene by spectroscopic and X-ray crystallographic analysis. The lethal dosage level of iso-grayanotoxin II in mice was lower than that of grayanotoxin III.     

Stereo- and regioselective hydroxylation of grindelic acid derivatives by Aspergillus niger

Stereo- and regioselective hydroxylation of grindelane derivatives on position 3beta was catalyzed by cultures of Aspergillus niger. Grindelic acid (1), methyl grindelate (2), 15-hydroxy-7(8)-en-9alpha,13(S)-oxide-ent-labdane (3) and 7alpha,8alpha-epoxymethylgrindelate (4) were bioconverted into the corresponding 3beta-hydroxy derivatives as the only biotransformation products. 13(S),15-dihydroxy-8(9)-en-ent-labdane (5) remained unreacted under the same conditions. The conformational and electronic studies of the substrates are discussed.     

Reactions of (Triphenylsilyl)ethylene Oxide with Grignard Reagents (and with MgBr(2)). A Reinvestigation

Reactions of (triphenylsilyl)ethylene oxide (1) with simple Grignard reagents such as EtMgBr and PhMgBr have been reported to yield crystalline hydroxysilanes assigned as the alpha-hydroxy silanes expected from beta opening of the epoxide. Reinvestigation of these reactions showed that the hydroxysilanes were the beta-hydroxy silanes 4 and 7 expected from a rearrangement-trapping sequence; a bromohydrin, assigned as the alpha-bromo-beta-hydroxy silane 9 from alpha opening, and (triphenylsilyl)acetaldehyde (8) were also formed.     

Synthesis and enzymatic kinetic resolution of alpha,alpha-disubstituted cyclic hydroxy nitriles

Herein, we describe the diastereoselective synthesis of five- and six-membered alpha,alpha-disubstituted cyclic beta-hydroxy nitriles and their resolution via enzymatic transesterification. By this method, all possible stereoisomers were obtained in enantiopure form and high yield.     

An Efficient Procedure for the Diastereoselective Dehydration of beta-Hydroxy Carbonyl Compounds by CeCl(3).7H(2)O/NaI System

The dehydration of beta-hydroxy ketones and beta-hydroxy esters is a synthetically useful method for the conversion of these compounds to the corresponding alpha,beta-unsaturated derivatives. Cerium(III) chloride heptahydrate in combination with sodium iodide in refluxing acetonitrile acts as an efficient reagent for this conversion. The present procedure, which utilizes cheap and "friendly" reagents, offers the corresponding (E)-enones in good yields as the only isolable products.     

Expeditious copper-catalyzed conjugate 1,4-addition of bromo[2-(1,3-dioxolan-2-yl)ethyl]magnesium to alpha,beta-cycloalkenones and subsequent transformations

Expeditious CuI-catalyzed conjugate 1,4-addition of bromo[2-(1,3-dioxolan-2-yl)ethyl]magnesium to the five-, six-, seven-, and eight-membered alpha,beta-cycloalkenones is described. The reaction times are decreased dramatically compared to CuBr-(CH(3))(2)S catalysis. The resulting ketoacetals were subsequently cyclized to bicyclic beta-hydroxy ketones and alpha,beta-enones, followed by further transformations.     

Catalytic asymmetric syntheses and biological activities of singly dehydroxylated 19-nor-1alpha,25-dihydroxyvitamin D(3) A-ring analogs in cancer cell differentiation and apoptosis

BACKGROUND: 1alpha,25-Dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)) has been shown to modulate not only proliferation and differentiation, but also apoptosis in malignant cells, indicating that it could be useful for treating cancer. Little information is available concerning the structural motifs of the 1alpha, 25(OH)(2)D(3) molecule responsible for modulation of differentiation and apoptosis, however. We set out to synthesize singly dehydroxylated A-ring analogs of 19-nor-1alpha,25(OH)(2)D(3) in a catalytic asymmetric fashion, and to investigate their biological activities in leukemia HL-60 cells. RESULTS: A series of singly dehydroxylated 19-nor-1alpha,25-dihydroxyvitamin D(3) A-ring analogs were synthesized using a combinatiorial sequence of regioselective propiolate-ene reaction and catalytic asymmetric carbonyl-ene cyclization. Surprisingly, the analogs could be clearly divided into two categories; one group, bearing 1alpha-hydroxy or 3beta-hydroxy groups in the A-ring, were potent differentiators and the second group, bearing 1beta-hydroxy or 3alpha-hydroxy groups, were potent stimulators of apoptosis. CONCLUSIONS: We have clearly identified the structural motifs of 19-nor-1alpha,25(OH)(2)D(3) analogs responsible for differentiation and apoptosis in HL-60 cells. These findings will provide useful information not only for development of therapeutic agents for treatment of leukemia and other cancers, but also for structure-function studies of 1alpha,25(OH)(2)D(3).     

Asymmetric synthesis of beta-hydroxy acid via stereoselective dirhodium(II)-catalyzed C-H insertion of alpha-alkoxydiazoketone

A new methodology for the asymmetric synthesis of beta-hydroxy acid was developed. Dirhodium(II)-catalyzed C-H insertion of alpha-alkoxydiazoketone (3), which was prepared from primary alkyl halide (1) and readily available chiral alpha-hydroxy acid (2), gave stereoselectively 2,5-cis-disubstituted 3(2H)-furanone (4). The Baeyer-Villiger reaction of 4 followed by treatment with an acid afforded chiral beta-hydroxy acid (6) with high optical purity.     

Unusual reaction of beta-hydroxy alpha-diazo carbonyl compounds with Cl3CCN/NaH and Rh(II)-catalyzed reaction of beta-trichloroacetylamino alpha-diazo carbonyl compounds

The hydroxyl group was directly converted into the trichloroacetylamino group by reacting beta-hydroxy alpha-diazo carbonyl compounds with Cl(3)CCN and NaH. Rh(II)-catalyzed reactions of the beta-amino alpha-diazo carbonyl compounds were discussed. [reaction: see text]     

From alcohols to sugars-how does the reactivity of alpha-hydroxyalkyl radicals change with structure? A quantitative examination by pulse radiolysis

Rate constants are reported for the 1-electron reduction of the azo dye Orange II in water (pH 7.0) by 10 different alpha-hydroxy radicals. The radicals were created by pulse radiolysis of aqueous solutions of the corresponding alcohol/sugar. The rate constants varied from 1 x 10(8) to 2.7 x 10(9) mol(-1) dm(3) s(-1) and radicals with beta-hydroxy groups had the lowest rate constant. The reaction was found to be controlled by the reduction potentials of the radicals, with steric influences having little effects. Good fits of the data were obtained using the Marcus equation with lambda =140 kJ/mol.     

Synthesis of C3-symmetric tris(beta-hydroxy amide) ligands and their Ti(IV) complex-catalyzed enantioselective alkynylation of aldehydes

[reaction: see text]. A series of new chiral C3-symmetric tris(beta-hydroxy amide) ligands have been synthesized via the reaction of 1,3,5-benzenetricarboxylic chloride and optically pure amino alcohols (up to 96% yield). The asymmetric catalytic alkynylation of aldehydes with these new C3-symmetric chiral tris(beta-hydroxy amide) ligands and Ti (O(i)'Pr)4 was investigated. Ligand 4c synthesized from (1R,2S)-(-)-2-amino-1,2-diphenylethanol is effective for the enantioselective alkynylation of various aldehydes, and high enantioselectivity was obtained with aromatic aldehydes and alpha,beta-unsaturated aldehyde (up to 92% ee).     

Alkaloid synthesis using chiral delta-amino beta-ketoesters: a stereoselective synthesis of (-)-lasubine II

[reaction: see text]A highly stereoselective asymmetric synthesis of the quinolizidinealkaloid (-)-lasubine II from a delta-amino beta-hydroxy ketone, a new polyfunctionalized chiral building block, is described.     

Asymmetric Samarium-Reformatsky Reaction of Chiral alpha-Bromoacetyl-2-oxazolidinones with Aldehydes

The samarium(II) iodide mediated asymmetric Reformatsky-type reaction of chiral 3-bromoacetyl-2-oxazolidinones with various aldehydes was studied. A series of chiral 4-substituted 2-oxazolidinones 1-3 and 5,5-disubstituted "SuperQuat" oxazolidinones 4-5 were employed as chiral auxiliaries of the alpha-bromoacetic acid. The reaction of 1 with various aldehydes gave the alpha-unbranched beta-hydroxy carboximides in good yields with high diastereomeric excess values (up to >99% de). The majority of the reaction product derived from 5,5-diphenyl SuperQuat 5 were highly crystallinity; a single recrystallization yielding a diastereomerically pure product with the other diastereomer not detectable by spectroscopic methods. The absolute configurations of the beta-hydroxy carboximides were determined by signs of optical rotations of the corresponding known ethyl esters referring to the literature values. Hydrolytic cleavage of the appended of beta-hydroxy moieties from the auxiliary SuperQuats was readily achieved under mild conditions using lithium hydroxide; the corresponding carboxylic acids and the returned SuperQuats were obtained in good yields without any evidence of racemization. The first step of the reaction is the reduction of the alpha-bromo group to produce the samarium enolate, which adds to an aldehyde. The absolute configuration of the adduct (7i) derive from benzaldehyde was found to be R, with the samarium enolate favoring the transition state predicted from chelation control of the reagent; this is in analogy to the discussion that has been used for the corresponding titanium enolate. The stereochemistry of the reaction may be explained by incorporating the Nerz-Stormes-Thornton chair transition structure model.     

Synergistic extraction of cobalt (II) by beta hydroxy naphthaldoxime and neutral donors

Liquid - liquid extraction of Cobalt (II) from aqueous hydrochloric acid medium by the use of oxime derivative of beta-hydroxy naphthaldehyde in o-xylene medium is being reported. The ligand was synthesized and characterized in our laboratory. The typical pH range of extraction of Co (II) by the ligand - donor combination was seen to be between 8 - 9. The effect of different donors like dimethyl sulphoxide (DMSO), trioctyl phosphine oxide (TOPO) and bis(2-ethylhexyl) phosphonate and the effect of various diluents on the extraction of Co(II) by the present method were studied in detail. The binary adduct formation constant (log kex) in the organic phase was found to be 3.182. The overall equilibrium constant (log K) for the ternary species [Co(A)(DMSO)(Cl)], [Co(A)(TOPO)(Cl)] and [Co(A)(phosphonate)(Cl)] were estimated to be 6.42, 6.22 and 6.25 respectively. The trend in equilibrium constants were in accordance with their basic character, i.e., (DMSO > or = TOPO approximately/= phosphonate). The results were extrapolated in the determination of Cobalt in pharmaceutical drugs and cobalt bearing ore samples.     

Total synthesis of (15R)- and (15S)-F(2t)-isoprostanes by a biomimetic process using the cyclization of acyclic dihydroxylated octa-5,7-dienyl radicals

We report a new route to F(2t)-IsoP (formerly named 8-epi-PGF(2alpha)) using a biomimetic radical cyclization of a highly functionalized C20 precursor. The strategy employed gives a beta-hydroxy free radical followed by molecular oxygen trapping, which is an unusual method for quenching carbon free radicals. We observed the formation of unique diastereoisomers (15R)- and (15S)-F(2t)-IsoP. This result is consistent with a strong stereoelectronic control associated with a steric effect initiated by the side chains alpha and omega on the cyclopentane ring.     

New mixed phosphonate esters by transesterification of pinacol phosphonates and their use in aldehyde and ketone coupling reactions with nonstabilized phosphonates

Alkylpinacol phosphonates were prepared by rhodium-catalyzed olefin hydrophosphorylation, and attempted alpha-deprotonation of the pinacol derived alkyl phosphonates resulted in ring cleavage. The propensity of the alkylpinacol phosphonates to undergo ring opening was exploited to prepare phosphonic acid monomethyl esters in high yield by transesterification in acidulated methanol. Esterification and alkylation with aldehydes or ketones gave beta-hydroxy mixed phosphonate esters. tert-Butyl and benzylic phosphonate ester protective groups were introduced to improve the efficiency and functional group compatibility of beta-hydroxy phosphonate saponification. The beta-hydroxy phosphonic acid monomethyl esters were dehydrated with diisopropylcarbodiimide, which gave oxaphosphetane intermediates that collapse to an olefin. The overall reaction sequence complements the arsenal of Horner-Wadsworth-Emmons-type coupling reactions.     

Catalytic hydrogenation of alpha,beta-epoxy ketones to form beta-hydroxy ketones mediated by an NADH coenzyme model

[reaction: see text] The hydrogenation of alpha,beta-epoxy ketones can be mediated by a catalytic amount of BNAH or BNA(+)Br(-) to form corresponding beta-hydroxy ketones in high yield. Na2S2O4 is used as the reducing agent to convert BNA(+)Br(-) to BNAH. A radical mechanism has been proposed to understand many observations of this catalytic reaction.     

Unexpected stereorecognition in nitrilase-catalyzed hydrolysis of beta-hydroxy nitriles

Biocatalytic enantioselective hydrolysis of beta-hydroxy nitriles to corresponding (S)-enriched beta-hydroxy carboxylic acids has been achieved for the first time by an isolated nitrilase bll6402 from Bradyrhizobium japonicum USDA110. This offers a new "green" approach to optically pure beta-hydroxy nitriles and beta-hydroxy carboxylic acids. The observed remote stereorecognition is surprising because this nitrilase shows no enantioselectivity for the hydrolysis of alpha-hydroxy nitriles such as mandelonitrile.     

Carbon-carbon bond-forming enantioselective synthesis of chiral organosilicon compounds by rhodium/chiral diene-catalyzed asymmetric 1,4-addition reaction

[reaction: see text] A new synthetic method for chiral organosilicon compounds through a rhodium-catalyzed asymmetric 1,4-addition of arylboronic acids to beta-silyl alpha,beta-unsaturated carbonyl compounds has been developed. By employing (R,R)-Bn-bod* as a ligand, a range of arylboronic acids can be coupled with these substrates in very high enantiomeric excess. The resulting beta-silyl 1,4-adducts can be converted to beta-hydroxy carbonyl compounds or allylsilanes while retaining their stereochemical information.     

Nitrile biotransformations for the synthesis of highly enantioenriched beta-hydroxy and beta-amino acid and amide derivatives: a general and simple but powerful and efficient benzyl protection strategy to increase enantioselectivity of the amidase

Biotransformations of a number of racemic beta-hydroxy and beta-amino nitrile derivatives were studied using Rhodococcus erythropolis AJ270, the nitrile hydratase and amidase-containing microbial whole cell catalyst, under very mild conditions. The overall enantioselectivity of nitrile biotransformations was governed predominantly by the amidase whose enantioselectivity was switched on remarkably by an O- and a N-benzyl protection group of the substrates. While biotransformations of beta-hydroxy and beta-amino alkanenitriles gave low yields of amide and acid products of very low enantiomeric purity, introduction of a simple benzyl protection group on the beta-hydroxy and beta-amino of nitrile substrates led to the formation of highly enantioenriched beta-benzyloxy and beta-benzylamino amides and acids in almost quantitative yield. The easy protection and deprotection operations, high chemical yield, and excellent enantioselectivity render the nitrile biotransformation a useful protocol in the synthesis of enantiopure beta-hydroxy and beta-amino acids.