Sodium 2-mercaptoethanesulfonate in reversible adduct formation and water solubilization

Sodium 2-mercaptoethanesulfonate (MESNA, coenzyme M) forms 1:1 covalent adducts with highly pi-electron deficient heterocycles. The addition is caused by the thiol function, and the adducts become water soluble as sulfonates. 1H NMR spectroscopy has been used to obtain information about electronic and steric effects on the equilibria between 2-pyrimidinones and their 1:1 MESNA adducts. The adducts are potential prodrugs for biologically interesting 2-pyrimidinones.     

Rapid intramolecular heterolytic dihydrogen activation by a four-membered heterocyclic phosphane-borane adduct

A four-membered cyclic intramolecular phosphane-borane adduct activates dihydrogen to yield the respective ethylene-bridged zwitterionic phosphonium-hydridoborate system, which reduces benzaldehyde.     

Novel hypervalent complexes of main-group metals by intramolecular ligand-->metal electron transfer

New fascinating electronic features of the simple diketoamine chelate ligand HN[CH2C(tBu)=O]2 (1) are described. Unexpectedly, the corresponding trianionic amido-dienolate form of 1 is capable of reducing main-group metal atoms M after initial coordination and intramolecular L-->M two-electron transfer and of stabilizing main-group elements in unusual low oxidation states. This is impressively shown by the synthesis and structural characterization of the novel Ge and Sn complexes 4-6 by redox reactions of lithiated 1 with the corresponding metal halides GeCl4 and MCl2 (M=Ge, Sn). Surprisingly, conversion of tris-lithiated 1 with GeCl4 readily consumes two molar equivalents of GeCl4 and results in the formation of the neutral GeCl3 complex 4 and GeCl2. The former represents the second example of a structurally characterized neutral octahedrally coordinated germanium compound. Reaction of dilithiated 1 with GeCl2 does not lead to the expected ClGe(+2) complex but affords the novel dimeric germylene 5, whereas similar reaction using SnCl2 furnishes the monomeric stannylene (ClSn(+2) complex) 2 and elemental tin due to the higher oxidation potential of Sn(+2). Unexpectedly, a similar redox reaction of dilithiated 1 with PbCl2 furnishes the first air- and water-stable lithium 1,2-diketoimine-enolate 7 and elemental lead. Compound 7 is tetrameric in the solid state and consists of a strongly distorted Li4O4 cubic core with trigonal-bipyramidal coordinated Li+ ions.     

Reactions of stereocontrolled intramolecular carbocyclization of levoglucosenone adduct with isoprene

An intramolecular carbocyclization was found of levoglucosenone adduct with isoprene providing a fused cyclobutane. The intramolecular oxacyclization of the adduct was performed under the treatment with I₂, H₃PO₄, SOCl₂, and Pd/C leading to 1,4-epoxide. Methods were developed of radical and anionic (by Ferrier method) transformation of the adduct into chiral trans- and cis-decalins.     

Formation and structure of a novel enediyne-RNA base covalent adduct

The structure of an unusual covalent adduct formed by thiol-activated neocarzinostatin chromophore (NCS-chrom) and a RNA-DNA hybrid having an overhang of four unpaired residues at the 3'-end of the RNA strand has been elucidated by MS and NMR spectroscopic analyses. Unlike previously characterized adducts formed by NCS-chrom on the sugar residue of the DNA target, this adduct has been found to be on one of the uracil bases in the RNA overhang. Covalent linkage is between C-6 of the post-activated NCS-chrom and C-5 of the uracil. A novel mechanism involving adduction of the NCS-chrom C-6 radical, generated by 2-mercaptoethanol activation, to C-5 of the uracil at the U9 position of the RNA 11-mer, oxidation by dioxygen, reduction by the thiol, and subsequent dehydration is proposed for adduct formation.     

Thermally reversible photochromic behaviour of new naphthopyrans involving an intramolecular [2+2] cyclization reaction

New 4-(2,2-diphenylethenyl)naphthopyrans were synthesized and their photochromic behaviour in solution were studied under continuous UV light irradiation conditions. Although only one coloured photoproduct was expected to be formed, due to the naphthopyran substitution pattern, NMR analysis on degassed UV irradiated solutions, performed at low temperature, showed the formation of different compounds. Among them, the main product is formed through an intramolecular [2+2] cyclization reaction and show thermally reversible photochromic properties.     

Formation of intramolecular rings in ferramonocarbollide complexes

Addition of PPh 2Cl and Tl[PF 6] to CH 2Cl 2 solutions of [N(PPh 3) 2][6,6,6-(CO) 3- closo-6,1-FeCB 8H 9] ( 1) affords the isomeric B-substituted species [6,6,6-(CO) 3- n-(PHPh 2)- closo-6,1-FeCB 8H 8] [ n = 7 ( 2a) or 10 ( 2b)]. Deprotonation (NaH) of the phosphine ligand in 2a, with subsequent addition of [IrCl(CO)(PPh 3) 2] and Tl[PF 6], yields the neutral, zwitterionic complex [6,6,6-(CO) 3-4,7-mu-{Ir(H)(CO)(PPh 3) 2PPh 2}- closo-6,1-FeCB 8H 7] ( 3), which contains a B-P-Ir- B ring. Alternatively, deprotonation using NEt 3, followed by addition of HC[triple bond]CCH 2Br, affords [6,6,6-(CO) 3-7-(PPh 2CCMe)- closo-6,1-FeCB 8H 8] ( 4). Addition of [Co 2(CO) 8] to CH 2Cl 2 solutions of the latter gives [6,6,6-(CO) 3-7-(PPh 2-{(mu-eta (2):eta (2)-CCMe)Co 2(CO) 6})- closo-6,1-FeCB 8H 8] ( 5), which contains a {C 2Co 2} tetrahedron. In the absence of added substrates, deprotonation of the PHPh 2 group in compounds 2, followed by reaction of the resulting anions with CH 2Cl 2 solvent, affords [6,6,6-(CO) 3- n-(PPh 2CH 2Cl)- closo-6,1-FeCB 8H 8] [ n = 7 ( 6a) or 10 ( 6b)] plus [6,6-(CO) 2-6,7-mu-{PPh 2CH 2PPh 2}- closo-6,1-FeCB 8H 8] ( 7, formed from 2a), of which the latter species possesses an intramolecular B-P-C-P- Fe ring. Addition of Me 3NO to CH 2Cl 2 solutions of 2a causes loss of an Fe-bound CO ligand and formation of [6,6-(CO) 2-6,7-mu-{NMe 2CH 2PPh 2}- closo-6,1-FeCB 8H 8] ( 8), which incorporates a B-P-C-N- Fe ring. A similar reaction in the presence of ligands L yields [6,6-(CO) 2-6-L-7-(PPh 2CH 2Cl)- closo-6,1-FeCB 8H 8] [L = PEt 3 ( 9) or CNBu (t) ( 10)], in addition to 8.     

Thermally reversible hydrogels via intramolecular folding and consequent self-assembly of a de novo designed peptide

A small de novo designed peptide (MAX3) is described that exhibits complete thermoreversible self-assembly into a hydrogel network. Importantly, a prerequisite to hydrogelation is that the peptide must first fold into a conformation conducive to self-assembly. At ambient temperature, MAX3 is unfolded, resulting in a low viscosity aqueous solution. On increasing the temperature, the peptide undergoes a unimolecular folding event, affording an amphiphilic beta-hairpin that consequently self-assembles into a hydrogel network. Increasing the temperature serves to dehydrate the nonpolar residues of the unfolded peptide and trigger folding via hydrophobic collapse. Cooling the resultant hydrogel results in beta-hairpin unfolding and consequent complete dissolution of the hydrogel. The temperature at which folding and consequent self-assembly into a rigid hydrogel occur can be tuned by altering the hydrophobicity of the peptides.     

Thermal intramolecular cycloaddition of 4-alkenylfulvene; highly regio- and diastereoselective formation of [4+2] adduct

4-Alkenylfulvenes were prepared by the annulation of 1,4-ynediones and allylidenetriphenylphosphorane and subjected to a thermal reaction. Highly regio- and stereoselective [4+2] cycloaddition is accomplished with 4-((R)-3-benzyloxypent-4-en-1-yl)fulvene and the resulting adduct is transformed into bicyclo[3.3.0]octene derivative.     

Formation of a N2-dG:N2-dG carbinolamine DNA cross-link by the trans-4-hydroxynonenal-derived (6S,8R,11S) 1,N2-dG adduct

Michael addition of trans-4-hydroxynonenal (HNE) to deoxyguanosine yields diastereomeric 1,N(2)-dG adducts in DNA. When placed opposite dC in the 5'-CpG-3' sequence, the (6S,8R,11S) diastereomer forms a N(2)-dG:N(2)-dG interstrand cross-link [Wang, H.; Kozekov, I. D.; Harris, T. M.; Rizzo, C. J. J. Am. Chem. Soc.2003, 125, 5687-5700]. We refined its structure in 5'-d(G(1)C(2)T(3)A(4)G(5)C(6)X(7)A(8)G(9)T(10)C(11)C(12))-3'·5'-d(G(13)G(14)A(15)C(16)T(17)C(18)Y(19)C(20)T(21)A(22)G(23)C(24))-3' [X(7) is the dG adjacent to the C6 carbon of the cross-link or the α-carbon of the (6S,8R,11S) 1,N(2)-dG adduct, and Y(19) is the dG adjacent to the C8 carbon of the cross-link or the γ-carbon of the HNE-derived (6S,8R,11S) 1,N(2)-dG adduct; the cross-link is in the 5'-CpG-3' sequence]. Introduction of (13)C at the C8 carbon of the cross-link revealed one (13)C8→H8 correlation, indicating that the cross-link existed predominantly as a carbinolamine linkage. The H8 proton exhibited NOEs to Y(19) H1', C(20) H1', and C(20) H4', orienting it toward the complementary strand, consistent with the (6S,8R,11S) configuration. An NOE was also observed between the HNE H11 proton and Y(19) H1', orienting the former toward the complementary strand. Imine and pyrimidopurinone linkages were excluded by observation of the Y(19)N(2)H and X(7) N1H protons, respectively. A strong H8→H11 NOE and no (3)J((13)C→H) coupling for the (13)C8-O-C11-H11 eliminated the tetrahydrofuran species derived from the (6S,8R,11S) 1,N(2)-dG adduct. The (6S,8R,11S) carbinolamine linkage and the HNE side chain were located in the minor groove. The X(7)N(2) and Y(19)N(2) atoms were in the gauche conformation with respect to the linkage, maintaining Watson-Crick hydrogen bonds at the cross-linked base pairs. A solvated molecular dynamics simulation indicated that the anti conformation of the hydroxyl group with respect to C6 of the tether minimized steric interaction and predicted hydrogen bonds involving O8H with C(20)O(2) of the 5'-neighbor base pair G(5)·C(20) and O11H with C(18)O(2) of X(7)·C(18). These may, in part, explain the stability of this cross-link and the stereochemical preference for the (6S,8R,11S) configuration.     

A novel intramolecular reversible reaction between the hydroxyl group and isobutenylene chain in a cyclophane-type macrocycle

A novel Hg²⁺ ion induced reversible ring contraction was achieved employing the intramolecular reaction of isobutylene with an aromatic hydroxyl group of cyclophane; reversibility of the reaction was facilitated by excess addition of NaBH₄ which also resulted in complexation. The ring contraction and expansion was monitored by UV-VIS absorption, and by fluorescence and ¹H NMR spectra. Switchable fluorescence behavior (on—off—on) was observed when the ring-size was tuned from a 19-membered ring to an 18-membered and vice versa. This fine tuning has the potential to be applied in the construction of new supramolecular devices.     

Luminescence on-off switching via reversible interconversion between inter- and intramolecular aurophilic interactions

Reversible interconversion between inter- and intramolecular AuAu interactions induces luminescence on/off switching in solid state. For the gold(I) photoluminescence system, intermolecular aurophilic interaction is a more significant factor than intramolecular aurophilic interaction.     

Conformational analysis in the reversible intramolecular [2+2] photocycloaddition of diphenylbicyclo[4.2.0]oct-3-ene-2,5-diones

An irradiation of diphenylbicyclo[4.2.0]oct-3-ene-2,5-diones bearing variously substituted Me groups resulted in the reversible intramolecular [2+2] cycloaddition between the excited enedione CC double bond and the facing endo-phenyl ring to exclusively give pentacyclotetradeca-10,12-diene-2,7-diones. The equilibrated product ratios were much dependent on the substitution pattern of the Me-groups as well as the irradiated wavelength. The regiochemistry of these photoadditions was elucidated on the basis of the restricted conformation of the starting enediones.     

Formation of N-alkoxyindole framework: intramolecular heterocyclization of 3-alkoxyimino-2-arylalkylnitriles mediated by ferric chloride

A variety of functionalized N-alkoxyindole-3-carbonitrile derivatives are achieved under remarkably mild conditions by applying a FeCl3-mediated intramolecular heterocyclization of 3-alkoxyimino-2-arylalkylnitriles. This novel synthesis allows the N-moiety on the side chain to be annulated to the benzene ring as the final synthetic step, which enables the functionalization of the benzenoid portion of the indole at an early stage of the synthesis.     

Reassessment of N2 activation by low-valent Ti-amide complexes: a remarkable side-on bridged bis-N2 adduct is actually an arene adduct

The complex {(TMEDA)₂Li}{[Ti(N(TMS)₂)₂]₂(μ-η²:η²-N₂)₂} (5-Li) is the only transition metal N₂ complex ever reported with two side-on N₂ adducts. In this report, the similarity of 5-Li to a new inverse sandwich toluene adduct {(PhMe)K}{[Ti(N(TMS)₂)₂]₂(μ-PhMe)} (6-K) necessitated a re-examination of the structure of 5-Li. Through a reassessment of the original disordered crystal data of 5-Li and new independent syntheses brought about through revisitation of the original reaction conditions, 5-Li has been re-assigned as an inverse sandwich toluene adduct, {(TMEDA)₂Li}{[Ti(N(TMS)₂)₂]₂(μ-PhMe)} (6-Li). The original crystal data could be fitted almost equally well to structural solutions as either 5-Li or 6-Li, and this study highlights the importance of a holistic examination of modeled data and the need for secondary/complementary analytical methods in paramagnetic inorganic syntheses, especially when presenting unique and unexpected results. In addition, further examination of reduction reactions of Ti[N(TMS)₂]₃ and [(TMS)₂N]₂TiCl(THF) in the presence of KC₈ revealed rich solvent- and counterion-dependent chemistry, including several degrees of N₂ activation (bridging nitride complexes, terminal bridging N₂ complexes) as well as ligand C–H activation.

The complex {(TMEDA)₂Li}{[Ti(N(TMS)₂)₂]₂(μ-η²:η²-N₂)₂} (5-Li) was the only transition metal N₂ complex ever reported with two side-on N₂ adducts. Reanalysis of 5-Li has revealed that it is an inverse-sandwich toluene adduct, not an N₂ adduct.     

主族元素取代的11-钨铜杂多配合物的合成、表征及性质研究

合成了ⅡA,ⅣA,ⅤA族元素为取代原子的3个系列钨铜杂多配合物.经ICP,TG曲线确定其化学式为K8[CuZ(OH2)W11O39].xH2O和K17,18[Z′(CuW11O39)2].xH2O(Z=Mg,Ca;Z′=Sr,Ba,Sn,Pb,Sb,Bi).通过TG-DTA,IR,XRD,XPS,183W-NMR等手段对合成配合物结构进行了表征,并对其进行了讨论.结果表明,新配合物具有典型的Keggin结构,且主族元素进入到配合物的骨架中.由于新配合物中CuⅡ具有顺磁性,导致XPS,183W-NMR的测试结果表现出特殊性;用循环伏安法测定了新配合物的电化学性质,表明均为可逆氧化还原过程,还对导电性和热稳定性进行了研究.