Asymmetric synthesis of aza-diospongin A as an iNOS inducer

The synthesis of the aza-analogue of diospongin A is described. The key steps in the synthetic sequence are Mitsunobu inversion, cross olefin metathesis and intramolecular aza-Michael addition reactions. The biological activity of this new analogue was also evaluated in the induction of nitric oxide synthase and was found to be better when compared to its natural counterpart.     

Through hydrogen-bond vibrational coupling in hydrogen-bonding chains of 4-pyridones with implications for peptide amide I absorptions: density functional theory compared with transition dipole coupling

We present B3LYP/D95** calculations on the C=O and N-H couplings in H-bonded chains of 4-pyridones. 14C-substitutions are used to decouple various vibrations for purposes of illustration. The coupled C=O vibrations bear analogy to the amide I bands of proteins and peptides. The coupling of the C=O's occurs primarily via the cooperative H-bonds rather than transition dipole coupling (TDC), as demonstrated by the fact that (1) the couplings are greater than previously reported for similar studies on formamides despite the larger distance between the C=O's in the pyridone chains (TDC coupling decreases with distance) and (2) the red shifts (also greater than for formamides) can be attributed to the changes in the geometries (particularly the C=O bond lengths) of the individual 4-pyridones in the H-bonding chains induced by the H-bonds and resulting polarization of the monomers.     

Thiocyanate complexes of the group 12 metals with pyridine-2-carboxamide: Synthesis and structural characterization

Three complexes of picolinamide (pyridine-2-carboxamide, pia) and metal thiocyanates, M(SCN)₂, (M = Zn, Cd, Hg), namely two polymorphs of bis(picolinamide-N,O)-bis-(thiocyanato-N)zinc(II) (1a and 1b), catena-[bis(μ-thiocyanato-S,N)-picolinamide-N,O-cadmium(II)] (2) and bis[(μ₂-thiocyanato-S-thiocyanato-S-picolinamide-N,O)mercury(II)] (3) have been prepared and characterized by spectroscopic, thermal and X-ray crystallographic methods. The IR and thermal data correlate with the structures of the complexes in the solid state. The vibration bands of diagnostic value are compared to the values of the free ligands.     

One‐Pot Sequential Propargylation/Cycloisomerization: A Facile [4+2]‐Benzannulation Approach to Carbazoles

A novel one‐pot [4+2]‐benzannulation approach to substituted carbazoles is accomplished by acid‐catalyzed C3‐propargylation of 2‐alkenyl/aryl indoles with 1‐aryl propargylic alcohols, followed by cycloisomerization. A variety of 2‐alkenylated indoles and 2‐aryl/heteroaryl indoles successfully participated in this tandem reaction with 1‐aryl/heteroaryl propargylic alcohols to provide diversely substituted and annulated carbazoles, as well as an aza[5]helicene.     

Synthesis of a diarylheptanoid, (+)-centrolobine

A chiron approach for the total synthesis of (+)-centrolobine has been described from the commercially available aldehyde 3 employing an acid-catalyzed stereoselective formation of tetrahydropyran ring as the key step. The desired molecule was accomplished in eight steps with 62% overall yield.     

On the Stability of PtIV Pro‐Drugs with Haloacetato Ligands in the Axial Positions

The design of Pt^IV pro‐drugs as anticancer agents is predicated on the assumption that they will not undergo substitution reactions before entering the cancer cell. Attempts to improve the cytotoxic properties of Pt^IV pro‐drugs included the use of haloacetato axial ligands. Herein, we demonstrate that Pt^IV complexes with trifluoroacetato (TFA) or dichloroacetato (DCA) ligands can be unstable under biologically relevant conditions and readily undergo hydrolysis, which results in the loss of the axial TFA or DCA ligands. The half‐lives for Pt^IV complexes with two TFA or DCA ligands at pH 7 and 37 °C range from 6 to 800 min, which is short relative to the duration of cytotoxicity experiments that last 24–96 h. However, complexes with two monochloroacetato (MCA) or acetato axial ligands are stable under biologically relevant conditions. The loss of the axial ligands depends primarily on the electron‐withdrawing strength of the axial ligands, but also upon the nature of the equatorial ligands. We were unable to find obvious correlations between the structures of the Pt^IV complexes and the rates of decay of the parent compounds. The X‐ray crystal structures of the bis‐DCA and bis‐MCA Pt^IV derivatives of oxaliplatin did not reveal any significant structural differences that could explain the observed differences in stability.     

A modular look at Farkas’ identities

Recently H. Farkas introduced a new simple arithmetic function and found an identity which involves this function. It is immediate to rewrite this identity as an identity between modular forms and reprove it in this way. We discuss natural generalizations of Farkas’ identity. Surprisingly, in a certain sense, there is only one identity which is an exact analogue of that found by Farkas. At the same time, we present a way to produce infinitely many similar identities. As an application, we obtain a result on non-vanishing of the central critical value of L-functions associated to a cusp Hecke eigenform. Supported by NSF grant DMS-0700933.     

Synthesis and Properties of the Alkyl/Aryl Germanium Dioximates Containing Ge─O Bond: Stability Factors—A Theoretical Approach

The reactions of R₂GeCl₂ and R₃GeCl with 9,10‐phenanthrenequinone dioxime in 1:1 and 1:2 molar ratios to form a series of organogermanium complexes of the general formula R₂GeL and (R₃Ge)₂L [R=Me, Et, Ph] have been investigated. The physical and spectral properties of all derivatives are described. In addition, the nature of Ge─O bond has been studied by using the DFT/B3LYP method.