Cu(II) coordination chemistry of patellamide derivatives: possible biological functions of cyclic pseudopeptides

Two synthetic derivatives of the naturally occurring cyclic pseudooctapeptides patellamide A-F and ascidiacyclamide, that is, H(4)pat(2), H(4)pat(3), as well as their Cu(II) complexes are described. These cyclic peptide derivatives differ from the naturally occurring macrocycles by the variation of the incorporated heterocyclic donor groups and the configuration of the amino acids connecting the heterocycles. The exchange of the oxazoline and thiazole groups by dimethylimidazoles or methyloxazoles leads to more rigid macrocycles, and the changes in the configuration of the side chains leads to significant differences in the folding of the cyclic peptides. These variations allow a detailed study of the various possible structural changes on the chemistry of the Cu(II) complexes formed. The coordination of Cu(II) with these macrocyclic species was monitored by high-resolution electrospray mass spectrometry (ESI-MS), spectrophotometric (UV/Vis) and circular dichroic (CD) titrations, and electron paramagnetic resonance (EPR) spectroscopy. Density functional theory (DFT) calculations and molecular mechanics (MM) simulations have been used to model the structures of the Cu(II) complexes and provide a detailed understanding of their geometric preferences and conformational flexibility. This is related to the Cu(II) coordination chemistry and the reactivity of the dinuclear Cu(II) complexes towards CO(2) fixation. The variation observed between the natural and various synthetic peptide systems enables conclusions about structure-reactivity correlations, and our results also provide information on why nature might have chosen oxazolines and thiazoles as incorporated heterocycles.     

Diterpenoids of terrestrial origin

This review covers the isolation and chemistry of the diterpenoids from terrestrial as opposed to marine sources and includes labdanes, clerodanes, abietanes, pimaranes, kauranes, gibberellins, cembranes and their cyclization products and taxanes. There are 161 references.     

High-temperature measurements of the reactions of OH with a series of ketones: acetone, 2-butanone, 3-pentanone, and 2-pentanone

The overall rate constants for the reactions of hydroxyl radicals (OH) with a series of ketones, namely, acetone (CH(3)COCH(3)), 2-butanone (C(2)H(5)COCH(3)), 3-pentanone (C(2)H(5)COC(2)H(5)), and 2-pentanone (C(3)H(7)COCH(3)), were studied behind reflected shock waves over the temperature range of 870-1360 K at pressures of 1-2 atm. OH radicals were produced by rapid thermal decomposition of the OH precursor tert-butyl hydroperoxide (TBHP) and were monitored by the narrow line width ring dye laser absorption of the well-characterized R(1)(5) line in the OH A-X (0, 0) band near 306.69 nm. The overall rate constants were inferred by comparing the measured OH time histories with the simulated profiles from the detailed mechanisms of Pichon et al. (2009) and Serinyel et al. (2010). These measured values can be expressed in Arrhenius form as k(CH3COCH3+OH) = 3.30 × 10(13) exp(-2437/T) cm(3) mol(-1) s(-1), k(C2H5COCH3+OH )= 6.35 × 10(13) exp(-2270/T) cm(3) mol(-1) s(-1), k(C2H5COC2H5+OH) = 9.29 × 10(13) exp(-2361/T) cm(3) mol(-1) s(-1), and k(C3H7COCH3+OH) = 7.06 × 10(13) exp(-2020/T) cm(3) mol(-1) s(-1). The measured rate constant for the acetone + OH reaction from the current study is consistent with three previous experimental studies from Bott and Cohen (1991), Vasudevan et al. (2005), and Srinivasan et al. (2007), within ±20%. Here, we also present the first direct high-temperature rate constant measurements of 2-butanone + OH, 3-pentanone + OH, and 2-pentanone + OH reactions. The measured values for the 2-butanone + OH reaction are in close accord with the theoretical calculation from Zhou et al. (2011), and the measured values for the 3-pentanone + OH reaction are in excellent agreement with the estimates (by analogy with the H-atom abstraction rate constants from alkanes) from Serinyel et al. Finally, the structure-activity relationship from Kwok and Atkinson (1995) was used to estimate these four rate constants, and the estimated values from this group-additivity model show good agreement with the measurements (within ~25%) at the present experimental conditions.     

Cationic cryptand complexes of tin(II)

A series of cationic cryptand complexes of tin(II), [Cryptand[2.2.2]SnX][SnX(3)] (10, X = Cl; 11, X = Br; 12, X = I) and [Cryptand[2.2.2]Sn][OTf](2) (13), were synthesized by the addition of cryptand[2.2.2] to a solution of either tin(II) chloride, iodide, or trifluoromethanesulfonate. The complexes could also be synthesized by the addition of the appropriate trimethylsilyl halide (or pseudohalide) reagent to a solution of tin(II) chloride and cryptand[2.2.2]. The complexes were characterized using a variety of techniques including NMR, Raman, and temperature-dependent M?ssbauer spectroscopy, mass spectrometry, and X-ray diffraction.     

Effect of exchange interaction on spin dephasing in a double quantum dot

We measure singlet-triplet dephasing in a two-electron double quantum dot in the presence of an exchange interaction which can be electrically tuned from much smaller to much larger than the hyperfine energy. Saturation of dephasing and damped oscillations of the spin correlator as a function of time are observed when the two interaction strengths are comparable. Both features of the data are compared with predictions from a quasistatic model of the hyperfine field.     

Polarization and readout of coupled single spins in diamond

We study the coupling of a single nitrogen-vacancy center in diamond to a nearby single nitrogen defect at room temperature. The magnetic dipolar coupling leads to a splitting in the electron spin resonance frequency of the nitrogen-vacancy center, allowing readout of the state of a single nitrogen electron spin. At magnetic fields where the spin splitting of the two centers is the same, we observe a strong polarization of the nitrogen electron spin. The amount of polarization can be controlled by the optical excitation power. We combine the polarization and the readout in time-resolved pump-probe measurements to determine the spin relaxation time of a single nitrogen electron spin. Finally, we discuss indications for hyperfine-induced polarization of the nitrogen nuclear spin.     

The role of botrydienediol in the biodegradation of the sesquiterpenoid phytotoxin botrydial by Botrytis cinerea

The biotransformation of botrydienediol (6) labelled with deuterium on carbons C-10 and C-15 has been studied. This has led to modification of some previous assumptions about the biodegradative route of botrydial. The [10-²H,15-²H]-botry-1(9)-4-diendiol (12) was transformed into dehydrobotrydienediol derivatives 13-15 but it was not incorporated into secobotryane skeleton (7). In addition, three new sesquiterpenoids have been isolated, which shed further light on the secondary metabolites of Botrytis cinerea. From the point of view of persistence of these toxins in the food chain, the easy biotransformation and different biodegradative routes of botrydial (1), seem to indicate that the toxin may not persist in the plant for a long time as it will be metabolized by the fungi and the plant.     

Steroids: partial synthesis in medicinal chemistry

This article reviews the progress in the chemistry of the steroids that was published between January and December 2004. The reactions and partial synthesis of estrogens, androgens, pregnanes, cholic acid derivatives, cholestanes and vitamin D analogues are covered. There are 127 references.     

Steroids: partial synthesis in medicinal chemistry

This article reviews the progress in the chemistry of the steroids that was published between January and December 2005. The reactions and partial synthesis of estrogens, androgens, pregnanes, bile acid derivatives, cholestanes and vitamin D analogues are covered. There are 139 references.     

Diterpenoids

This review covers the isolation and structures of diterpenoids, including labdanes, clerodanes,pimaranes, abietanes, kauranes, cembranolides, taxanes and marine diterpenoids. The literature from January to December 2005 is reviewed, and 195 references are cited.