Stereochemistry Of Compounds Research Articles

Three New Apo‐tirucallols with Six‐Membered Hemiacetal from Meliaceae.

Three new apo-tirucallols, 1alpha,7alpha-diacetoxyl-17alpha-20S-21,24-epoxy-apotirucall-14-ene-3alpha,23R,24S,25-tetraol (1), 7alpha-acetoxyl-17alpha-20S-21,24-epoxy-apotirucall-14-ene-3a,23R,24S,25-tetraol (2), 7alpha-acetoxyl-17alpha-20S-21,24-epoxy-apotirucall-14-en-3-one-23R,24S,25-triol (3) were obtained from the plants of the family Meliaceae. Their configurations were elucidated on the basis of extensive 1D and 2D NMR techniques in CD3OD solution. The equilibrium of the six-membered ring hemiacetal at side chain is also discussed. Finally, the stereochemistry of compound 1 was demonstrated by X-ray crystallography. (C) 2002 Elsevier Science Ltd. All rights reserved.

Three new apo-tirucallols with six-membered hemiacetal from Meliaceae

Three new apo-tirucallols, 1α,7α-diacetoxyl-17α-20 S-21,24-epoxy-apotirucall-14-ene-3α,23 R,24 S,25-tetraol ( 1 ), 7α-acetoxyl-17α-20 S-21,24-epoxy-apotirucall-14-ene-3α,23 R,24 S,25-tetraol ( 2 ), 7α-acetoxyl-17α-20 S-21,24-epoxy-apotirucall-14-en-3-one-23 R,24 S,25-triol ( 3 ) were obtained from the plants of the family Meliaceae. Their configurations were elucidated on the basis of extensive 1D and 2D NMR techniques in CD 3OD solution. The equilibrium of the six-membered ring hemiacetal at side chain is also discussed. Finally, the stereochemistry of compound 1 was demonstrated by X-ray crystallography.

Cucubalactam and Brachystemin E, Two New Compounds from Caryophyllaceae

A new pyrrolidone peroxide, named cucubalactam (1), and a new octacyclopeptide, named brachystemin E (2), have been isolated from Caryophyllaceae plants, Cucubalus baccifer and Brachystemma calycinum, respectively. Their structures were determined by spectral methods, especially by 1D and 2D NMR techniques. The stereochemistry of compound (2) was demonstrated by X-Ray crystallograph.

Synthesis of 8-Substituted 7-Azarutaecarpines

The synthesis of 8-substituted 7-azarutaecarpines 2 is described. These compounds were prepared by Fischer indolization of 3-amino-2-(1-phenylhydrazonoethyl)-4(3 H)-quinazolinone 5, followed by cyclocondensation with a series of aliphatic, araliphatic or aromatic aldehydes and formic acid or a Vilsmeier–Haack reagent. The stereochemistry of compounds 2 was investigated by 1H NMR spectroscopy. It was found that the 8-substituents assume a quasi-axial position on the flattened boat conformation of ring C of 2, with the exception of ortho substituted phenyl groups, which occupy quasi-equatorial positions. Semi-empirical MO calculations support these conformational preferences.

Two novel secoergosterols from the fungus Tylopilus plumbeoviolaceus.

Two novel secoergosterols, 3beta-hydroxy-8alpha,9alpha-oxido-8, 9-secoergosta-7,9(11),22-triene (tylopiol A) (1) and 3beta-hydroxy-8alpha,9alpha-oxido-8,9-secoergosta-7,22 -dien-12-one (tylopiol B) (2), were isolated from the fresh fruit bodies of Tylopilus plumbeoviolaceus, along with three known compounds, ergosta-7,22-dien-3beta-ol, uridine, and allitol. Their structures were elucidated by NMR techniques, including (1)H NMR, (13)C NMR, HMQC, HMBC, and MS. The structure and stereochemistry of compound 1 were demonstrated by X-ray crystallography.

Pyrrolidines, Pyrrolines and Pyrroles from 1,4-Diaryl-2,3-dinitro-1,3-butadienes via a 5-endo-trig Cyclization

The reactions between 1,4-diaryl-2,3-dinitro-1,3-butadienes 1a-d and primary alkylamines gave high yields of N-alkyl-2,5-diaryl-3-alkylamino-4-nitropyrrolidines 2 as pure all-trans diastereomers via an unusually favoured 5-endo-trig ring closure. The stereochemistry of compounds 2 has been attributed through an X-ray crystal structure analysis of the acetyl derivative 5 of 2ai. Amine elimination from 2 gave the N-alkyl-2,5-diaryl-3-nitro-3-pyrrolines 3 which could be easily aromatized to the corresponding pyrroles 4.

Prieurianin-Type Tetranortriterpenoids from the Bark of Dysoxylum hainanense

From the ethanolic extract of the bark of Dysoxylum hainanense Merr., three new seco-tetranortriterpenoids structurally related to prieurianin, dysoxylumins A (1), B (2) and C (3) were isolated. Their structures were elucidated on the basis of 1D and 2D NMR techniques. The structure and stereochemistry of compound 1 were demonstrated by X-Ray crystallography.

A revised structure for (-)-dihydropertusaric acid, a gamma-butyrolactone acid from the lichen punctelia microsticta

The gamma-butyrolactone acid (1) and two known compounds, (-)-isomuronic acid and the tridepside gyrophoric acid, have been isolated from the lichen Punctelia microsticta. The structure and stereochemistry of compound 1 were determined on the basis of spectroscopic evidence and molecular modeling. Spectroscopic and physical data of 1 and (-)-dihydropertusaric acid, previously isolated from the lichen Pertusaria albescens, showed that both are the same compound, although for the latter the epimeric structure 2 has been proposed.

Cytotoxic polyacetylenes from the marine sponge Petrosia sp.

Three C46 (1-3) and three C30 (4-6) polyacetylenic alcohols with cytotoxic activity against a small panel of human solid-tumor cell lines have been isolated from the marine sponge Petrosia sp. Although compound 1 was identified as the stereoisomer of petrocortyne A, the structures of compounds 2-5 have not been previously reported and were established by spectral methods. Compound 6 was identified as the known compound petrosiacetylene D. The stereochemistry of compounds 1-5 was determined by the modified Mosher's method.

New Products from the Reactions of Artemisinin with Ammonia and Amines

Reaction of artemisinin (1) with ammonia, methylamine, dimethylamine, and allylamine afforded five unexpected products 2-6, in addition to the previously reported compounds 7-12. The identities of the new compounds were established from their spectral data, by chemical derivatization and by comparison with published reports. The stereochemistries of compounds 5 and 6 were confirmed by single-crystal X-ray analysis.

Structural analogues of cumambrin B from the flower of Chrysanthemum boreale.

The structural analogues of cumambrin B (1, 2, 3, 4) were isolated from the flower of Chrysanthemum boreale Makino. The structures of compounds were determined by two-dimensional 1H-1H COSY and 13C-1H COSY spectra with the aid of homonuclear and heteronuclear double resonance experiment. The stereochemistry of compounds has been verified from single crystal X-ray diffraction of cumambrin A (2). The antimicrobial activities of these guaianolides have been studied.

Synthesis and Complexation Behavior of the Functionalized Tripodal Phosphane cis,cis‐1,3,5‐Tris(cyano)‐1,3,5‐tris(diphenylphosphanyl)‐cyclohexane (tdppcycn)

AbstractThe synthesis of the novel potentially bistripodal ligand cis‐cis‐1,3,5‐tris(cyano)‐1,3,5‐tris(diphenylphosphanyl)cyclohexane (tdppcycn) (6) is described. Starting from the tricarboxylic acid cis,cis‐1,3,5‐C6H9(COOH)3 (1), which is converted stepwise into the triacid chloride cis,cis‐1,3,5‐C6H9(COCl)3 (2), the triphenyl ester cis,cis‐1,3,5‐C6H9(COOPh)3 (3), the tricarboxamide cis,cis‐1,3,5‐C6H9(CONH2)3 (4), and the tricarbonitrile cis,cis‐1,3,5‐C6H9(CN)3 (5), we obtained tdppcycn (6) by α‐deprotonation of 5 followed by treatment with ClPPh2 in good yield. Treatment of 6 with Mo(CO)3(‐C7H8) and Ir(PPh3)2(CO)Cl gave octahedral Mo(tdpp‐cycn)(CO)3 (7) and pentacoordinate Ir(tdppcycn)(CO)Cl (8), respectively, with a facially P‐coordinated tdppcycn ligand. The stereochemistry of compounds 2–8 was established by 1H‐, 13C‐, 31P‐NMR, and IR spectroscopy. An X‐ray crystal structure analysis of complex 8 confirms the trigonal‐bipyramidal ground‐state structure in the solid state.

Cyclometallated platinum(II) and platinum(IV) compounds of N-benzylidene-2-chlorobenzylamine. Crystal structure of [PtMe(PPh 3)(C 6H 4CHNCH 2C 6H 4C1-2)

The cyclometallated compound [PtMe(SMe 2)(C 6H 4CHNCH 2C 6H 4C1-2)] ( 1) undergoes a displacement reaction with PPh 3 to yield a cyclometallated platinum(II) compound [PtMe(PPh 3)(C 6H 4CHNCH 2C 6H 4C1-2)] ( 2), which has been characterized crystallographically. Complex 2 crystallizes in the monoclinic space group C2/ c, with a = 38.402(4) Å, b = 7.993(3) Å, c = 18.563(3) Å, β = 101.34(3)° and Z = 8. The reaction of 1 with 1,2-bis (diphenylphosphino)ethane (dppe) yields [PtMe(dppe)(C 6H 4CHNCH 2C 6H 4C1-2)]( 3) containing an unidentate C donor imine ligand and a chelating diphosphine. Oxidative addition of methyl iodide to 1 yields a cyclometallated platinum(IV) compound [PtMe 2I(SMe 2)(C 6H 4CHNCH 2C 6H 4C1-2)] ( 4), which undergoes a displacement reaction of SMe 2 by PPh 3 to yield [PtMe 2I(PPh 3)(C 6H 4CHNCH 2C 6H 4C1-2)] ( 5). Compound 5 can also be obtained by oxidative addition of methyl iodide to 2. The stereochemistry of compounds 4 and 5 is discussed.

Dimethyldioxirane Oxidation of 3‐Arylidenechromanones

AbstractOxidation of the (E) and (Z) isomers of the 3‐arylidenechromanones 5 by isolated dimethyldioxirane (as acetone solution) at ambient temperature resulted in the formation of the spiro epoxides trans‐ and cis‐6, respectively, in moderate yields (23–51%), together with considerable amounts (16–40%) of the 3‐aroylchromones 7 from both (E)‐ and (Z)‐5 isomers. Minor products, namely 3‐(α‐hydroxy‐4‐methoxy‐benzyl)‐4H‐1‐benzopyran‐4‐one (8b), 1a,7a‐dihydro‐7a‐(α‐hydroxy‐4‐methylbenzyl)‐7H‐oxireno[b][1]benzopyran‐7‐one (9d), and the 1a,7a‐dihydro‐7a‐aroyl‐7H‐oxireno[b][1]‐benzopyran‐4‐ones 10a–c have also been isolated and characterized. Presumably, the formation of 3‐aroylchromones 7 can be attributed to competitive allylic oxidation with dimethyldioxirane to afford first the 3‐(α‐hydroxyarylmethyl)‐chromones 8, whose secondary alcohol functionality is subsequently oxidized by dimethyldioxirane to give the 3‐aroylchromones 7. Further oxidation of the latter by dioxirane affords the epoxides 10, as established by a control experiment. Alternatively, first oxidation of 8 to yield epoxide 9 and subsequent oxidation of the alcohol functionality to afford the overoxidized product 10 cannot be disposed of on grounds of our product data. Nonetheless, despite the moderate yields of the desirable chromanone epoxides 6, the stereoselective oxidation directly of the chromanones by dimethyldioxirane offers a convenient preparation. Relative configuration and stereochemistry of compounds 6–10 were elucidated by NMR spectroscopy and AM1 calculations. magnified image

Influence of analyte stereochemistry and basicity on peak shape of basic compounds in high-performance liquid chromatography with reversed-phase columns, using pyridine and alkyl-substituted derivatives as probe compounds

Column efficiency, peak asymmetry and retention factor of a series of sixteen compounds comprising pyridine and some alkyl-substituted derivatives, with p K a values ranging from 5.17 to 6.74 is reported on a RP-HPLC column previously shown to be especially suitable for the analysis of basic compounds. Compound stereochemistry in close vicinity of the basic group is found to influence peak shape strongly: however, stereochemistry at more remote positions is also of some significance. The effect of p K a on peak shape is discussed in the light of measurements of the degree of protonation of the compounds in the methanolic mobile phase as well as water.

Conformation Dependent Cyclizations of 1,3,3,5-Tetraphenylpentane-1,5-dione

The molecular and crystal structure of 1,3,3,5-tetraphenylpentane-1,5-dione (I) obtained from direct methods and anisotropically refined by the least-squares method shows that the two 3,3-phenyl groups force the molecule into a conformation suitable for formation of cyclic products and intermediates. Compound I crystallizes in P1 group with lattice parameters a = 8.444(1), b = 10.195(2), c = 14.618(2) Å, α = 75.52(2)°, β = 73.22(1)°, γ = 65.47(1)°. Photochemically and thermally found was the system I ↔ II. The reaction of 1,5-dione I with phenylmagnesium bromide gives the 2,3-dihydropyran derivative III, whereas complex hydrides give a mixture of IV and VI. On treatment with magnesium, the diketone I gives diol VIII. Chlorine (Cl2) reacts with compound I to give the mono-, di-, and tetrachloro derivatives XII, XIII, and XIV, respectively. Bromine (Br2) produces 3,5-dibromo-4H-pyran derivative XVIII, whereas I2 only catalyzes the formation of 4H-pyran V. The formylation of dione I with dimethylformamide and POCl3 gives the 4H-pyran-3-carbaldehyde XX. Probable mechanisms of the reactions investigated and the stereochemistry of compounds VI, VIII, XIII, and XIV are discussed.

10α-hydroxymethylsparteine, a new type of quinolizidine alkaloid from Genista sessilifolia

10α-Hydroxymethylsparteine (1), a novel type of quinolizidine alkaloid with a 16-carbon atom skeleton, was isolated from the aerial parts of Genista sessilifolia DC. The position of the hydroxymethyl substituent and the stereochemistry of compound 1 were established by analysis of its spectroscopic data.

Kaurene derivatives from Lasianthea fruticosa, revision of stereochemistry of related compounds

Two new kaurene diterpenes, 12α-angeloyloxy and 12α-senecioyloxy-9,11-dehydro- ent-kaur-16-en-19-oic acids, have been isolated from Lasianthea fruticosa. The structures and stereochemistry of the compounds were determined on the basis of spectroscopic techniques and minor chemical transformation. The stereochemistry of a few similar compounds has been revised.

Synthesis and stereochemistry of compounds carrying two chiral alkylalkoxythiophosphoryl substituents on the phosphorus atom

1. Compounds containing a pseudochiral phosphorus atom have been prepared (bis(ethylethoxythiophosphoryl) phenylphosphinite, bis(ethylethoxythiophosphoryl) methylphosphonate, and bis(ethylethoxythiophosphoryl) phenylthiophosphonate). Their optically active stereoisomers have been obtained. 2. 31P-{1H} NMR spectroscopy has been used to show that the compounds obtained from racemic O-ethylethylthiophosphonic acid are a mixture of the three diastereoisomers (two meso-forms and the racemic d,ι form in the statistical ratio, 1∶2∶1.

New germacrane derivatives from Nanothamnus sericeous. X-Ray molecular structure of (1R,4R,5R,6R,10R)-1,10;4,5-diepoxy-11-hydroxygermacran-6-yl (Z)-2-methylbut-2-enoate

Four new closely related germacrane derivatives have been isolated from the acetone extract of Nanothamnus sericeous. Based on spectral data and some chemical evidence, the structures of these compounds have been established as (1R,4R,5R,6R,10R)-1,10;4,5-diepoxy-11-hydroxygermacran-6-yl (Z)-2-methylbut-2-enoate (1a), (4R,5R,6R)-4,5-epoxy-11-hydroxygermacr-1(10)-en-6-yl (Z)-2-methylbut-2-enoate (6a), (1R,4R,5R,6R,10S)-1,10;4,5-diepoxy-11-hydroxygermacrane-6,14-diyl bis-[(Z)-2-methylbut-2-enoate](7a), and 4ξ,5ξ,11-trihydroxygermacran-6-yl (Z)-2-methylbut-2-enoate (9a). The structure and stereochemistry of compound (1a) have been confirmed by X-ray crystallography.