Total synthesis of (+)-blastmycinone and formal synthesis of (+)-antimycin A3b

The formal synthesis of (+)-antimycin A_3b and the total synthesis of (+)-blastmycinone were achieved using, as a key step, a method developed by us for the synthesis of 2-methyl-1,3-diols via Ti(III)-mediated diastereo- and regioselective opening of trisubstituted 2,3-epoxy alcohols, to carry out the stereoselective construction of the hydroxy-acid segment. An interesting intramolecular radical translocation took place during the epoxide opening process transforming its vicinal PMB-ether in situ, into an ‘1,2-O-(p-methoxy)benzylidene’ ring.     

Studies on radical cyclization of 2,3-epoxy alcohols containing a β-(alkoxy)acrylate moiety using Cp2TiCl

Radical-mediated opening of chiral 2,3-epoxy alcohols, containing suitably positioned β-(alkoxy)acrylate moieties, using Cp₂TiCl triggered intramolecular cyclization to give tetrahydrofuran and tetrahydropyran moieties.     

Spectrophotometric investigation of Ti(IV) complexes of N-phenylacetylphenylhydroxylamine

N-Phenylacetylphenylhydroxylamine complexes of titanium(IV), yellow in color and extractable into chloroform, with metal:ligand ratios 1:2, 1:3, and 1:4, exist in the acidity ranges of 1–3, 4–7, and 7.5–9.0 N HCl, respectively. The compositions of the complexes were found out by Job's and molar ratio methods. The stepwise and overall formation constants were evaluated following extensions of Yatsimirskii's, Leden's and Harvey and Manning's methods. A computer was used for evaluation of the formation constants of the 1:3 system following the first method. A spectrophotometric method based on solvent extraction technique, for determination of trace amounts of titanium in the presence of diverse ions, has also been described.     

Sugar amino acid based scaffolds--novel peptidomimetics and their potential in combinatorial synthesis

To meet the growing demands for the development of new molecular entities for discovering new drugs and materials, organic chemists have started looking for new concepts to supplement traditional approaches. In one such approach, the expertise gained over the years in the area of organic synthesis and the rational drug-design concepts are combined together to create "nature-like" and yet unnatural organic molecules that are expected to provide leads in discovering new molecules. Emulating the basic principles followed by nature to build its vast repertoire of biomolecules, organic chemists are developing many novel multifunctional building blocks. Sugar amino acids constitute an important class of such polyfunctional scaffolds where the carboxyl, amino and hydroxyl groups provide an excellent opportunity for organic chemists to create structural diversities akin to nature's molecular arsenal. Recent advances in the area of combinatorial chemistry give unprecedented technological support for rapid compilations of sugar amino acid-based libraries exploiting the diversities of carbohydrate molecules and well-developed solid-phase peptide synthesis methods. This review chronicles the development of sugar amino acids as a novel class of peptidomimetic building blocks and their applications in generating desired secondary structures in peptides as well as in creating mimics of natural biopolymers.     

Dibutyltin(IV) complexes of the 5-[(E)-2-(Aryl)-1-diazenyl]-2-hydroxybenzoic acid ligand: an investigation of structures by X-ray diffraction, solution and solid state tin NMR, electrospray ionisation MS and assessment of in vitro cytotoxicity

A series of dibutylbis{5-[(E)-2-(aryl)-1-diazenyl]-2-hydroxybenzoato}tin(IV) complexes, Bu₂Sn(LH)₂, have been prepared and characterized by ¹H, ¹³C, ¹¹⁹Sn NMR and ESI mass spectrometry in solution. The structures of the complexes Bu₂Sn(L¹H)₂ (1), Bu₂Sn(L³H)₂ (3), Bu₂Sn(L⁴H)₂ (4), and Bu₂Sn(L⁶H)₂ (6) (L = 5-[(E)-2-(aryl)-1-diazenyl]-2-hydroxybenzoate: aryl = phenyl (L¹H), 3-methylphenyl (L³H), 4-methylphenyl (L⁴H) and 4-bromophenyl (L⁶H)) were determined by X-ray crystallography and ¹¹⁷Sn CP-MAS NMR spectroscopy in the solid state. In general, the complexes were found to adopt a skew-trapezoidal bipyramidal arrangement around the tin atom. In addition, there are weak bridging intermolecular Sn?O contacts in complexes 1 and 3, but not in 4 and 6, where one of the hydroxy oxygen atoms from a neighboring molecule coordinates weakly with the Sn atom, thereby completing a seventh coordination site in the extended Sn coordination sphere. The Sn?O distance is 3.080(2) and 3.439(2) Å in 1 and 3, respectively, which are significantly shorter than the sum of the van der Waals radii of the Sn and O atoms (∼3.8 Å). In 1, this Sn?O interaction links the molecules into polymeric chains. In 3, these interactions link pairs of molecules into head-to-head dimeric units. The in vitro cytotoxicity of compound 2 indicates better results than cisplatin and etoposide against seven well characterized human tumor cell lines.     

Studies directed towards the synthesis of antascomicin A: stereoselective synthesis of the C1-C21 fragment of the molecule

A stereoselective synthesis of the C1-C21 fragment of the non-immunosuppressive immunophilin-binding natural product, antascomicin A was achieved using, as key steps, highly stereoselective Aldol reactions to build the C1-C17 fragment and a Nozaki-Hiyama-Kishi reaction to couple it with the remaining C18-C21 moiety.     

Synthesis of (3R,4S,5S,9S)-3,5,9-trihydroxy-4-methylundecanoic acid δ-lactone

Radical-mediated opening of a chiral trisubstituted epoxy alcohol using cp₂TiCl furnished the ‘2-methyl-1,3-diol’ moiety with the desired stereochemistry, which led to a total synthesis of (3R,4S,5S,9S)-3,5,9-trihydroxy-4-methylundecanoic acid δ-lactone 1.     

Dinuclear zinc(II) complexes of tetraiminodiphenol macrocycles and their interactions with carboxylate anions and amino acids. Photoluminescence, equilibria, and structure

The reaction equilibria [H(4)L](2+) + Zn(OAc)(2) right harpoon over left harpoon [Zn(H(2)L)](2+) + 2HOAc (K(1)) and [Zn(H(2)L)](2+) + Zn(OAc)(2) right harpoon over left harpoon [Zn(2)L](2+) + 2HOAc (K(2)), involving zinc acetate and the perchlorate salts of the tetraiminodiphenol macrocycles [H(4)L(1)(-)(3)](ClO(4))(2), the lateral (CH(2))(n)() chains of which vary between n = 2 and n = 4, have been studied by spectrophotometric and spectrofluorimetric titrations in acetonitrile. The photoluminescence behavior of the complexes [Zn(2)L(1)](ClO(4))(2), [Zn(2)L(2)(H(2)O)(2)](ClO(4))(2), [Zn(2)L(2)(mu-O(2)CR)](ClO(4)) (R = CH(3), C(6)H(5), p-CH(3)C(6)H(4), p-OCH(3)C(6)H(4), p-ClC(6)H(4), p-NO(2)C(6)H(4)), and [Zn(2)L(3)(mu-OAc)](ClO(4)) have been investigated. The X-ray crystal structures of the complexes [Zn(2)L(2)(H(2)O)(2)](ClO(4))(2), [Zn(2)L(3)(mu-OAc)](ClO(4)), and [Zn(2)L(2)(mu-OBz)(OBz)(H(3)O)](ClO(4)) have been determined. The complex [Zn(2)L(2)(mu-OBz)(OBz)(H(3)O)](ClO(4)) in which the coordinated water molecule is present as the hydronium ion (H(3)O(+)) on deprotonation gives rise to the neutral dibenzoate-bridged compound [Zn(2)L(2)(mu-OBz)(2)].H(2)O. The equilibrium constants (K) for the reaction [Zn(2)L(2)(H(2)O)(2)](2+) + A(-) right harpoon over left harpoon [Zn(2)L(2)A](+) + 2H(2)O (K), where A(-) = acetate, benzoate, or the carboxylate moiety of the amino acids glycine, l-alanine, l-histidine, l-valine, and l-proline, have been determined spectrofluorimetrically in aqueous solution (pH 6-7) at room temperature. The binding constants (K) evaluated for these systems vary in the range (1-8) x 10(5).     

Optimization of the Visualization of Steroids Separated by OPLC

JPC – Journal of Planar Chromatography – Modern TLC - The acidic visualization methods most often used for steroids have been optimized and compared. Sulfuric acid at three different...