Oligonucleotide Analogues with a Nucleobase‐Including Backbone:, Part 6, 2‐Deoxy‐D‐erythrose‐Derived Phosphoramidites: Synthesis and Incorporation into 14‐Mer DNA Strands

Two modified DNA 14‐mers have been prepared, containing either a 2‐deoxy‐D ‐erythrose‐derived adenosine analogue carrying a C(8)−CH₂O group (deA*), or a 2‐deoxy‐D ‐erythrose‐derived uridine analogue, possessing a C(6)−CH₂O group (deU*). These nucleosides are linked via a phosphinato group between O−C(3′) (deA* and deU*) and O−C(5′) of one neighbouring nucleotide, and between C(8)−CH₂O (deA*), or C(6)−CH₂O (deU*) and O−C(3′) of the second neighbour. N⁶‐Benzoyl‐9‐(β‐D ‐erythrofuranosyl)adenine ( 3 ) and 1‐(β‐D ‐erythrofuranosyl)uracil ( 4 ) were prepared from D ‐glucose, deoxygenated at C(2′), and converted into the required phosphoramidites 1 and 2 . The modified tetradecamers 31 and 32 were prepared by solid‐phase synthesis. Pairing studies show a decrease in the melting temperature of 7 to 8 degrees for the duplexes 31 ⋅ 30 and 32 ⋅ 29 , as compared to the unmodified DNA duplex 29 ⋅ 30 . A comparison with the pairing properties of tetradecamers similarly incorporating deoxyribose‐ instead of the deoxyerythrose‐derived nucleotides evidences that the CH₂OH substituent at C(4′) has no significant effect on the pairing.     

Oligonucleosides with a Nucleobase‐Including Backbone,Part 4, A Convergent Synthesis of Ethynediyl‐Linked Adenosine Tetramers

Deprotection of the tetramer 24 , obtained by coupling the iodinated dimer 18 with the alkyne 23 gave the 8′,5‐ethynediyl‐linked adenosine‐derived tetramer 27 (Scheme 3). As direct iodination of C(5′)‐ethynylated adenosine derivatives failed, we prepared 18 via the 8‐amino derivative 17 that was available by coupling the imine 15 with the iodide 7 ; 15 , in its turn, was obtained from the 8‐chloro derivative 12 via the 4‐methoxybenzylamine 14 (Scheme 2). This method for the introduction of the 8‐iodo substituent was worked out with the N‐benzoyladenosine 1 that was transformed into the azide 2 by lithiation and treatment with tosyl azide (Scheme 1). Reduction of 2 led to the amine 3 that was transformed into 7 . 1,3‐Dipolar cycloaddition of 3 and (trimethylsilyl)acetylene gave 6 . The 8‐substituted derivatives 4a – d were prepared similarly to 2 , but could not be transformed into 7 . The known chloride 8 was transformed into the iodide 11 via the amines 9 and 10 . The amines 3 , 10 , and 16 form more or less completely persistent intramolecular C(8)N−H⋅⋅⋅O(5′) H‐bonds, while the dimeric amine 17 forms a ca. 50% persistent H‐bond. There is no UV evidence for a base‐base interaction in the protected and deprotected dimers and tetramers.     

Oligonucleosides with a Nucleobase‐Including Backbone,Part 3, Synthesis of Acetyleno‐Linked Adenosine Dimers

The adenosine‐derived dimers 14a – d and 15b – d have been prepared by coupling the protected 8‐iodoadenosines 3 and 13 with the C(5′)‐ethynylated adenosine derivatives 5 , 6 , 11 , and 12 (Scheme 4). Similarly, the 5′‐epimeric dimer 16 was prepared by coupling 3 with the alkyne 8 (Scheme 5). The propargylic alcohol 4 was transformed into the N‐benzoylated alkyne 5 and into the amine 6 , while the epimeric alcohol 7 was converted to the epimeric amine 8 and the 5′‐deoxy analogues 11 and 12 (Scheme 3). Cross‐coupling of the iodoadenosine 13 with the alkyne 5 to 14a was optimised; it is influenced by the N‐benzoyl and the Et₃SiO group of the alkyne, but hardly by the N‐benzoyl group of the 8‐iodoadenosine. The alkyne is most reactive when it is O‐silylated, but not N‐benzoylated. Cross‐coupling of the 5′‐deoxyalkynes proceeded more slowly. The dimers 14a – d , 15b – d , and 16 were obtained in good yields (Table 2). Deprotection of 14d and 16 led to 18 and 20 , respectively (Scheme 5). The diols 17 and 19 and the hexols 18 and 20 prefer the syn‐conformation in (D₆)DMSO, completely for unit II and ≥80% for unit I; they exhibit partially persistent intramolecular O(5′)−H⋅⋅⋅N(3) H‐bonds. The persistence increases from 18% (unit I of 19 ), 32% (unit II of 17 and 19 ), 45% (unit I of 17 ), 52% (unit II of 18 and 20 ), and 55% (unit I of 20 ) to 82% (unit I of 18 ).     

Oligonucleosides with a Nucleobase‐Including Backbone. Part 11

A linear and a convergent synthesis of uridine‐derived backbone‐base‐dedifferentiated (backbone including) oligonucleotide analogues were compared. The Sonogashira cross‐coupling of the alkyne 1 and the iodide 2 gave the dimer 4 that was C‐desilylated and again coupled with 2 to give the trimer 6 (Scheme 1). Repeating this linear sequence led to the pentamer 10 . Coupling yields were satisfactory up to formation of the trimer 6 , but decreased for the coupling to higher oligomers. Similarly, coupling of the alkynes 5, 7 , and 9 with the iodouridine 3 gave, in decreasing yields, the trimer 12 , tetramer 13 , and pentamer 14 , respectively. The dimeric iodouracil 20 was synthesized by coupling the alkyne 17 with the iodide 16 to the dimer 18 , followed by iodination at C(6/I) to 19 and O‐silylation (Scheme 2). The iodinated dimer 23 was prepared by iodinating and O‐silylating the known dimer 21 . Coupling of 20 and 23 with the dimer 5 , trimer 7 , and tetramer 9 gave the tetramers 8 and 13 , the pentamers 10 and 14 , and the hexamer 15 , respectively (Scheme 3). The oligomers up to the pentamer 14 were deprotected to provide the trimer 24 , tetramer 25 , and pentamer 26 (Scheme 4). There was no evidence for the heteropairing of the pentamer 26 and rA₇ , nor for the pairing of rU₅ and rA₇, while a UV melting experiment showed the beginning of a sigmoid curve for the interaction of rU₇ with rA₇. Therefore, the pentamer 26 does not pair more strongly with rA₇ than rU₅.     

Oligonucleosides with a Nucleobase‐Including Backbone,Part 7

The conformational analysis of 7 was carried out in (D₆)DMSO and in mixtures of (D₆)DMSO and CDCl₃ to evaluate the syn/anti conformations, relevant to the pairing propensity of this type of nucleotide analogue. The HO−C(5′) of unit I and of unit II of the dimer 7 form an intramolecular H‐bond to N(3). In (D₆)DMSO, the C(5′)−OH⋅⋅⋅N(3) H‐bond in unit I is partially broken, while that in unit II persists to a larger extent. The syn conformation prevails for unit I and particularly for unit II. The furanosyl moieties adopt predominantly a 2′‐endo conformation that is largely independent of the solvent.     

Regioselectivity of the 1,3‐Oxathiolane Formation in the Lewis Acid‐Catalyzed Reaction of Thioketones with Asymmetrically Substituted Oxiranes

The reactions of the aromatic thioketone 4,4′‐dimethoxythiobenzophenone ( 1 ) with three monosubstituted oxiranes 3a – c in the presence of BF₃⋅Et₂O or SnCl₄ in dry CH₂Cl₂ led to the corresponding 1 : 1 adducts, i.e., 1,3‐oxathiolanes 4a – b with R at C(5) and 8c with Ph at C(4). In addition, 1,3‐dioxolanes 7a and 7c , and the unexpected 1 : 2 adducts 6a – b were obtained (Scheme 2 and Table 1). In the case of the aliphatic, nonenolizable thioketone 1,1,3,3‐tetramethylindane‐2‐thione ( 2 ) and 3a – c with BF₃⋅Et₂O as catalyst, only 1 : 1 adducts, i.e. 1,3‐oxathiolanes 10a – b with R at C(5) and 11a – c with R or Ph at C(4), were formed (Scheme 6 and Table 2). In control experiments, the 1 : 1 adducts 4a and 4b were treated with 2‐methyloxirane ( 3a ) in the presence of BF₃⋅Et₂O to yield the 1 : 2 adduct 6a and 1 : 1 : 1 adduct 9 , respectively (Scheme 5). The structures of 6a , 8c , 10a , 11a , and 11c were confirmed by X‐ray crystallography (Figs. 1 – 5). The results described in the present paper show that alkyl and aryl substituents have significant influence upon the regioselectivity in the process of the ring opening of the complexed oxirane by the nucleophilic attack of the thiocarbonyl S‐atom: the preferred nucleophilic attack occurs at C(3) of alkyl‐substituted oxiranes (O−C(3) cleavage) but at C(2) of phenyloxirane (O−C(2) cleavage).     

2,2′‐Anhydro‐1‐(3′,5′‐di‐O‐acetyl‐β‐D‐arabinofuranosyl)uracil,a cyclouridine nucleoside with a C4′‐endo furanosyl conformation

2,2′‐Anhydro‐1‐(3′,5′‐di‐O‐acetyl‐β‐D‐arabinofuranosyl)uracil, C₁₃H₁₄N₂O₇, was obtained by refluxing 2′,3′‐O‐(methoxymethylene)uridine in acetic anhydride. The structure exhibits a nearly perfect C4′‐endo (⁴E) conformation. The best four‐atom plane of the five‐membered furanose ring is O—C—C—C, involving the C atoms of the fused five‐membered oxazolidine ring, and the torsion angle is only −0.4 (2)°. The oxazolidine ring is essentially coplanar with the six‐membered uracil ring [r.m.s. deviation = 0.012 (5) Å and dihedral angle = −3.2 (3)°]. The conformation at the exocyclic C—C bond is gauche–trans which is stabilized by various C—H...π and C—O...π interactions.     

Formation of 6,10‐Diphenyl‐Substituted Heptalene‐4,5‐dicarboxylates

It is shown that 4,8‐diphenylazulene ( 1 ) can be easily prepared from azulene by two consecutive phenylation reactions with PhLi, followed by dehydrogenation with chloranil. Similarly, a Me group can subsequently be introduced with MeLi at C(6) of 1 (Scheme 2). This methylation led not only to the expected main product, azulene 2 , but also to small amounts of product 3 , the structure of which has been determined by X‐ray crystal‐structure analysis (cf. Fig. 1). As expected, the latter product reacts with chloranil at 40° in Et₂O to give 2 in quantitative yields. Vilsmeier formylation of 1 and 2 led to the formation of the corresponding azulene‐1‐carbaldehydes 4 and 5 . Reduction of 4 and 5 with NaBH₄/BF₃ ? OEt₂ in diglyme/Et₂O 1 : 1 and BF₃ ? OEt₂, gave the 1‐methylazulenes 6 and 7 , respectively. In the same way was azulene 9 available from 6 via Vilsmeier formylation, followed by reduction of azulene‐1‐carbaldehyde 8 (Scheme 3). The thermal reactions of azulenes 1, 6 , and 7 with excess dimethyl acetylenedicarboxylate (ADM) in MeCN at 100° during 72 h afforded the corresponding heptalene‐4,5‐dicarboxylates 11, 12 , and 13 , respectively (Scheme 4). On the other hand, the highly substituted azulene 9 gave hardly any heptalene‐4,5‐dicarboxylate.     

The 7‐bromo derivative of 2‐amino‐2′‐deoxytubercidin fluorinated at the sugar moiety

The title compound, 2,4‐diamino‐5‐bromo‐7‐(2‐deoxy‐2‐fluoro‐β‐d ‐arabinofuranosyl)‐7H‐pyrrolo[2,3‐d]pyrimidine, C₁₁H₁₃BrFN₅O₃, shows two conformations of the exocyclic C4′—C5′ bond, with the torsion angle γ (O5′—C5′—C4′—C3′) being 170.1 (3)° for conformer 1 (occupancy 0.69) and 60.7 (7)° for conformer 2 (occupancy 0.31). The N‐glycosylic bond exhibits an anti conformation, with χ = −114.8 (4)°. The sugar pucker is N‐type (C3′‐endo; ³T₄), with P = 23.3 (4)° and τ_m = 36.5 (2)°. The compound forms a three‐dimensional network that is stabilized by several intermolecular hydrogen bonds (N—H...O, O—H...N and N—H...Br).     

Intra‐ and Intermolecular H‐Bonds of Alcohols in DMSO, 1H‐NMR Analysis of Inter‐Residue H‐Bonds in Selected Oligosaccharides: Cellobiose,Lactose, N,N′‐Diacetylchitobiose,Maltose, Sucrose,Agarose, and Hyaluronates

Inter‐residue H‐bonds of oligosaccharides in (D₆)DMSO have been assigned on the basis of a combined interpretation of the chemical shift (δ(OH)), coupling constant (J(H,OH)), and temperature dependence (Δδ(OH)/ΔT) of OH signals. Cellobiose, lactose, and N,N′‐diacetylchitobiose possess a completely persistent C(3)OH⋅⋅⋅OC(5′) H‐bond. Maltose is characterised by flip‐flop H‐bonds between HO−C(3) and HO−C(2′), and agarose by two weakly persistent inter‐residue H‐bonds. Sucrose forms an equilibrium of differently H‐bonded species, and hyaluronates possess four strong inter‐residue H‐bonds.     

Stereoselective Synthesis of [5‐[4,4,4,4′,4′,4′‐Hexafluoro‐N‐(2‐hydroxyethoxy)‐D‐valine]]‐ and [5‐[4,4,4,4′,4′,4′‐Hexafluoro‐N‐(2‐hydroxyethoxy)‐L‐valine]cyclosporin A

Addition of various amines to the 3,3‐bis(trifluoromethyl)acrylamides 10a and 10b gave the tripeptides 11a – 11f , mostly as mixtures of epimers (Scheme 3). The crystalline tripeptide 11f ₂ was found to be the N‐terminal (2‐hydroxyethoxy)‐substituted (R,S,S)‐ester HOCH₂CH₂O‐D ‐Val(F₆)‐MeLeu‐Ala‐O^tBu by X‐ray crystallography. The C‐terminal‐protected tripeptide 11f ₂ was condensed with the N‐terminus octapeptide 2b to the depsipeptide 12a which was thermally rearranged to the undecapeptide 13a (Scheme 4). The condensation of the epimeric tripeptide 11f ₁ with the octapeptide 2b gave the undecapeptide 13b directly. The undecapeptides 13a and 13b were fully deprotected and cyclized to the [5‐[4,4,4,4′,4′,4′‐hexafluoro‐N‐(2‐hydroxyethoxy)‐D ‐valine]]‐ and [5‐[4,4,4,4′,4′,4′‐hexafluoro‐N‐(2‐hydroxyethoxy)‐L ‐valine]]cyclosporins 14a and 14b , respectively (Scheme 5). Rate differences observed for the thermal rearrangements of 12a to 13a and of 12b to 13b are discussed.     

Oligonucleosides with a Nucleobase‐Including Backbone,Part 2, Synthesis and Structure Determination of Adenosine‐Derived Monomers

The synthesis and structure determination of adenosine‐derived monomeric building blocks for new oligonucleosides are described. Addition of Me₃Si‐acetylide to the aldehyde derived from the known partially protected adenosine 1 led to the epimeric propargylic alcohols 2 and 3 , which were oxidised to the same ketone 4 , while silylation and deprotection led to 7 and 9 (Scheme 1). Introduction of an I substituent at C(8) of the propargylic silyl ethers 10 and 11 was not satisfactory. The protected adenosine 12 was, therefore, transformed in high yield into the 8‐chloro derivative 13 by deprotonation and treatment with PhSO₂Cl; the iodide 15 was obtained in a similar way (Scheme 2). The 8‐Cl and the 8‐I derivatives 13 and 15 were transformed into the propargylic alcohols 17 , 18 , 25 , and 26 , respectively (Scheme 3). The propargylic derivatives 2 , 10 , 17 , 19 , 23 , 25 , and 27 were correlated, and their (5′R) configuration was determined on the basis of NOEs of the anhydro nucleoside 19 ; similarly, correlation of 3 , 11 , 18 , 20 , 24 , 26 , and 28 , and NOE's of 20 evidenced their (5′S)‐configuration.     

Oligonucleotide Analogues with a Nucleobase‐Including Backbone,Part 5, 2′‐Deoxy‐8‐(hydroxymethyl)adenosine‐ and 2′‐Deoxy‐6‐(hydroxymethyl)uridine‐Derived Phosphoramidites: Synthesis and Incorporation into 14‐Mer DNA Strands

The pairing propensity of new DNA analogues with a phosphinato group between O−C(3′) and a newly introduced OCH₂ group at C(8) and C(6) of 2′‐deoxyadenosine and 2′‐deoxyuridine, respectively, was evaluated by force‐field calculations and Maruzen model studies. These studies suggest that these analogues may form autonomous pairing systems, and that the incorporation of single modified units into DNA 14mers is compatible with duplex formation. To evaluate the incorporation, we prepared the required phosphoramidites 3 and 4 from 2′‐deoxyadenosine and 2′‐deoxyuridine, respectively. The phosphoramidite 5 was similarly prepared to estimate the influence of a CH₂OH group at C(8) on the duplex stability. The modified 14‐mers 6 – 9 were prepared by solid‐phase synthesis. Pairing studies show a decrease of the melting temperature by 2.5° for the duplex 13 ⋅ 9 , and of 6 – 8° for the duplexes 10 ⋅ 6 , 11 ⋅ 6 , 13 ⋅ 7 , and 14 ⋅ 8 , as compared to the unmodified duplexes.     

[2 + 3]‐Cycloadditions of Phosphonodithioformate S‐Methanides with CS,NN,and CC Dipolarophiles

The reaction of the methyl (dialkoxyphosphinyl)‐dithioformates (= methyl dialkoxyphosphinecarbodithioate 1‐oxides) 10 with CH₂N₂ at − 65° in THF yielded cycloadducts which eliminated N₂ between − 40 and − 35° to give the corresponding phosphonodithioformate S‐methanides ( =methylenesulfonium (dialkoxyoxidophosphino)(methylthio)methylides) 11 (Scheme 3). These reactive 1,3‐dipoles were intercepted by aromatic thioketones to yield 1,3‐dithiolanes. Whereas the reaction with thiobenzophenone ( 12b ) led to the sterically more congested isomers 15 regioselectively, a mixture of both regioisomers was obtained with 9H‐fluorene‐9‐thione ( 12a ). Trapping of 11 with phosphono‐ and sulfonodithioformates led exclusively to the sterically less hindered 1,3‐dithiolanes 16 and 18 , respectively (Scheme 4). In addition, reactive CC dipolarophiles such as ethenetetracarbonitrile, maleic anhydride, and N‐phenylmaleimide as well as the NN dipolarophile dimethyl diazenedicarboxylate were shown to be efficient interceptors of 11 (Scheme 5).     

Synthesis of Bis‐Heterocyclic 1H‐Imidazole 3‐Oxides from 3‐Oxido‐1H‐imidazole‐4‐carbohydrazides

The reaction of 1H‐imidazole‐4‐carbohydrazides 1 , which are conveniently accessible by treatment of the corresponding esters with NH₂NH₂?H₂O, with isothiocyanates in refluxing EtOH led to thiosemicarbazides (=hydrazinecarbothioamides) 4 in high yields (Scheme 2). Whereas 4 in boiling aqueous NaOH yielded 2,4‐dihydro‐3H‐1,2,4‐triazole‐3‐thiones 5 , the reaction in concentrated H₂SO₄ at room temperature gave 1,3,4‐thiadiazol‐2‐amines 6 . Similarly, the reaction of 1 with butyl isocyanate led to semicarbazides 7 , which, under basic conditions, undergo cyclization to give 2,4‐dihydro‐3H‐1,2,4‐triazol‐3‐ones 8 (Scheme 3). Treatment of 1 with Ac₂O yielded the diacylhydrazine derivatives 9 exclusively, and the alternative isomerization of 1 to imidazol‐2‐ones was not observed (Scheme 4). It is important to note that, in all these transformations, the imidazole N‐oxide residue is retained. Furthermore, it was shown that imidazole N‐oxides bearing a 1,2,4‐triazole‐3‐thione or 1,3,4‐thiadiazol‐2‐amine moiety undergo the S‐transfer reaction to give bis‐heterocyclic 1H‐imidazole‐2‐thiones 11 by treatment with 2,2,4,4‐tetramethylcyclobutane‐1,3‐dithione (Scheme 5).     

Synthesis,Crystal Structure and Hydrolysis of a Novel Anhydrogalactosucrose: 2′‐Methoxyl‐O‐1′,4′:3′,6′‐dianhydro‐β‐D‐fructofuranosyl 3,6‐anhydro‐4‐chloro‐4‐deoxy‐α‐D‐galactopyranoside

A novel anhydrogalactosucrose derivative 2′‐methoxyl‐O‐1′,4′:3′,6′‐dianhydro‐β‐D‐fructofuranosyl 3,6‐anhydro‐4‐chloro‐4‐deoxy‐α‐D‐galactopyranoside ( 4 ) was prepared from 3,6:1′,4′:3′,6′‐trianhydro‐4‐chloro‐4‐deoxy‐galactosucrose ( 3 ) via a facile method and characterized by ¹H NMR, ¹³C NMR and 2D NMR spectra. The single crystal X‐ray diffraction analysis shows that the title molecule forms a two thee‐dimensional network structure by two kinds of hydrogen bond interactions [O(2) H(2)···O(7), O(5) H(5)···O(8)]. Its stability was investigated by acid hydrolysis reaction treated with sulfuric acid, together with the formation of 1,6‐Di‐O‐methoxy‐4‐chloro‐4‐deoxy‐β‐D‐galactopyranose ( 5 ) and 2,2‐Di‐C‐methoxy‐1,4:3,6‐dianhydromannitol ( 6 ). According to the result, the relative stability of the ether bonds in the structure is in the order: C(1) O C(5)≈C(3′) O C(6′)≈C(1′) O C(4′)>C(3) O C(6)≈C(1) O C(2′)>C(2′) O C(5′).     

6‐Aza‐2′‐deoxy­uridine and N3‐anisoyl‐6‐aza‐2′‐deoxy­uridine

In 2‐(2‐deoxy‐β‐d ‐erythro‐pentofuranosyl)‐1,2,4‐triazine‐3,5(2H,4H)‐dione (6‐aza‐2′‐deoxy­uridine), C₈H₁₁N₃O₅, (I), the conformation of the glycosylic bond is between anti and high‐anti [χ = −94.0 (3)°], whereas the derivative 2‐(2‐deoxy‐β‐d ‐erythro‐pentofuranosyl)‐N⁴‐(2‐methoxy­benzoyl)‐1,2,4‐triazine‐3,5(2H,4H)‐dione (N³‐anisoyl‐6‐aza‐2′‐deoxy­uridine), C₁₆H₁₇N₃O₇, (II), displays a high‐anti conformation [χ = −86.4 (3)°]. The furanosyl moiety in (I) adopts the S‐type sugar pucker (²T₃), with P = 188.1 (2)° and τ_m = 40.3 (2)°, while the sugar pucker in (II) is N (³T₄), with P = 36.1 (3)° and τ_m = 33.5 (2)°. The crystal structures of (I) and (II) are stabilized by inter­molecular N—H⋯O and O—H⋯O inter­actions.     

Solid‐state 119Sn NMR and antitumor activity of bis [1,3‐bis (3‐oxapentamethylenecarbamoylthioacetato)‐1,1,3,3‐tetrabutyl‐1,3‐distannoxare], and the crystal structure of its bis‐ethanol solvate

The ¹¹⁹Sn cross polarization‐magic angle spinning NMR spectrum of bis[1,3‐bis(3‐oxapentamethylenecarbamoylthioacetato)‐1,1,3,3‐tetrabutyl‐1,3‐distannoxane], {[(C₄H₉)₂SnO₂CCH₂SC(O)N(CH₂CH₂)₂O]₂O}₂, which consists of two resonances of similar chemical shifts and symmetry (δ_iso = −152, −202 ppm; asymmetry, κ = 0.38), implies the existence of two five‐coordinate tin sites in the centrosymmetric dimer. The assignment has been corroborated by X‐ray diffraction analysis on the compound that has been crystallized from ethanol; the crystal structure shows two tin atoms in cis‐C₂SnO₃ trigonal‐bipyramidal coordination [C‐Sn‐C = 131.5(1), 131.3(2) °]. The analysis also reveals the presence of two lattice ethanol molecules that are hydrogen‐bonded to the dimer [OO = 2.779(5) Å]. When exposed to air, the distannoxane loses ethanol. The unsolvated distannoxane is more active than cis‐platin when screened against MCF‐7 (mammary cancer), EVSA‐T (mammary cancer), WiDr (colon cancer), IGROV (ovarian cancer), M19 MEL (melanoma), A498 (renal cancer) and H226 (lung cancer) cell lines. Copyright © 2000 John Wiley & Sons, Ltd.     

Domino‐Heck Reactions of Carba‐ and Oxabicyclic,Unsaturated Dicarboximides: Synthesis of Aryl‐Substituted,Bridged Perhydroisoindole Derivatives

The C? C coupling of the two bicyclic, unsaturated dicarboximides 5 and 6 with aryl and heteroaryl halides gave, under reductive Heck conditions, the C‐aryl‐N‐phenyl‐substituted oxabicyclic imides 7a – c and 8a – c (Scheme 3). Domino‐Heck C? C coupling reactions of 5, 6 , and 1b with aryl or heteroaryl iodides and phenyl‐ or (trimethylsilyl)acetylene also proved feasible giving 8, 9 , and 10a – c , respectively (Scheme 4). Reduction of 1b with LiAlH₄ (→ 11 ) followed by Heck arylation and reduction of 5 with NaBH₄ (→ 13 ) followed by Heck arylation open a new access to the bridged perhydroisoindole derivatives 12a , b and 14a , b with prospective pharmaceutical activity (Schemes 5 and 6).     

Methyl 4‐O‐β‐D‐mannopyranosyl β‐D‐xylopyranoside

Methyl β‐D‐mannopyranosyl‐(1→4)‐β‐D‐xylopyranoside, C₁₂H₂₂O₁₀, (I), crystallizes as colorless needles from water, with two crystallographically independent molecules, (IA) and (IB), comprising the asymmetric unit. The internal glycosidic linkage conformation in molecule (IA) is characterized by a ϕ′ torsion angle (O5′_Man—C1′_Man—O1′_Man—C4_Xyl; Man is mannose and Xyl is xylose) of −88.38 (17)° and a ψ′ torsion angle (C1′_Man—O1′_Man—C4_Xyl—C5_Xyl) of −149.22 (15)°, whereas the corresponding torsion angles in molecule (IB) are −89.82 (17) and −159.98 (14)°, respectively. Ring atom numbering conforms to the convention in which C1 denotes the anomeric C atom, and C5 and C6 denote the hydroxymethyl (–CH₂OH) C atom in the β‐Xylp and β‐Manp residues, respectively. By comparison, the internal glycosidic linkage in the major disorder component of the structurally related disaccharide, methyl β‐D‐galactopyranosyl‐(1→4)‐β‐D‐xylopyranoside), (II) [Zhang, Oliver & Serriani (2012). Acta Cryst. C 68 , o7–o11], is characterized by ϕ′ = −85.7 (6)° and ψ′ = −141.6 (8)°. Inter‐residue hydrogen bonding is observed between atoms O3_Xyl and O5′_Man in both (IA) and (IB) [O3_Xyl...O5′_Man internuclear distances = 2.7268 (16) and 2.6920 (17) Å, respectively], analogous to the inter‐residue hydrogen bond detected between atoms O3_Xyl and O5′_Gal in (II). Exocyclic hydroxymethyl group conformation in the β‐Manp residue of (IA) is gauche–gauche, whereas that in the β‐Manp residue of (IB) is gauche–trans.