Development of nonproprietary phosphine ligands for the Pd-catalyzed amination reaction

A new family of pyrazole and bi-pyrazole phosphine ligands are reported that perform efficiently in the Pd-catalyzed amination reaction. Of the ligands screened, ligand 1 emerged as the most compatible for couplings involving both primary and secondary amines with typical yields of 84-99%.     

Metal iodide mediated ring expansion of cyclopropanecarboxylic thioesters with imines

Metal iodide mediated three-component reactions of cyclopropanecarboxylic thioesters 1, aldehydes, and amines were developed. The initial products, pyrrolidines 2 were obtained in 39-73% yields, which could further be converted to lactams 4, via sequential reactions of a retro-aza-Michael addition and an intramolecular cyclization. This methodology provided facile access to analogs of both pyrrolidines 2 and lactams 4.     

Multifaceted Studies of the DNA Interactions and In Vitro Cytotoxicity of Anticancer Polyaromatic Platinum(II) Complexes

This study reports a detailed biophysical analysis of the DNA binding and cytotoxicity of six platinum complexes (PCs). They are of the type [Pt(P_L)(SS‐dach)]Cl₂, where P_L is a polyaromatic ligand and SS‐dach is 1S,2S‐diaminocyclohexane. The DNA binding of these complexes was investigated using six techniques including ultraviolet and fluorescence spectroscopy, linear dichroism, synchrotron radiation circular dichroism, isothermal titration calorimetry and mass spectrometry. This portfolio of techniques has not been extensively used to study the interactions of such complexes previously; each assay provided unique insight. The in vitro cytotoxicity of these compounds was studied in ten cell lines and compared to the effects of their R,R enantiomers; activity was very high in Du145 and SJ‐G2 cells, with some submicromolar IC₅₀ values. In terms of both DNA affinity and cytotoxicity, complexes of 5,6‐dimethyl‐1,10‐phenanthroline and 2,2′‐bipyridine exhibited the greatest and least activity, respectively, suggesting that there is some correlation between DNA binding and cytotoxicity.     

Solvatochromism of distyrylbenzene pairs bound together by [2.2]paracyclophane: evidence for a polarizable "through-space" delocalized state

A series of compounds were designed and synthesized to examine how through-space and through-bond electron delocalization respond to solvent effects. The general strategy involves the study of "dimers" of the distyrylbenzene chromophore held in close proximity by the [2.2]paracyclophane core and a systematic dissection of the chromophore into components with through-space and through-bond electronic delocalization. Steady state and time-resolved fluorescence spectroscopy in a range of solvents reveals a red-shift in emission and an increase in the intrinsic fluorescence lifetime for the emitting state in polar solvents when donor substituents are absent. We propose that through-space delocalization across the [2.2]paracyclophane core is more polarizable in the excited state, relative to the through-bond (distyrylbenzene based) excited state. When strong donors are attached to the distyrylbenzene chromophore, the charge transfer character of the distyrylbenzene-based excited state dominates fluorescence properties.     

Synthesis of a Type-VIβ-Turn Peptide Mimetic and Its Incorporation into a High-Affinity Somatostatin Receptor Ligand

The synthesis of a cis-Phe-Pro dipeptide mimetic is described, which adopts a type-VIβ-turn conformation. In this mimetic, the α-positions of Phe and Pro are joined by a CH₂CH₂ bridge, thereby forming a fused bicyclic system, and fixing a geometry similar to that seen in cis-Phe-Pro units in protein crystal structures. The dipeptide mimetic 20 was synthesized in optically pure form starting from (R)-α-allylproline ( 6 ; Schemes 1, 3, and 4), with a free carboxylic acid and an Fmoc-protected N-terminus, thereby allowing its incorporation into linear and cyclic peptides using standard solid-phase methods. The mimetic 20 was incorporated into the cyclic somatostatin analogue cyclo(-Phe = Pro-Phe-D -Trp-Lys-Thr-), where Phe = Pro represents the mimetic. This analogue shows a high affinity (pIC₅₀ 8.6) for somatostatin receptors on rat-brain cortex membranes. Based on NMR studies in aqueous solution, likely low-energy conformations for this analogue were deduced using restrained dynamic simulated annealing. The conformations found, which include a distorted type-II′ turn at D -Trp-Lys, are similar to low-energy conformations deduced elsewhere for cyclo(-Phe-Pro-Phe-D -Trp-Lys-Thr-), as well as to those seen in crystal structures of the somatostatin analogue octreotide.     

High-throughput purification of combinatorial libraries II: Automated separation of single diastereomers from a 4-amido-pyrrolidone library containing intentional diastereomer pairs

A 4-amido-pyrrolidone library that was intentionally synthesized as pairs of diastereomers was produced by solution-phase parallel syntheses and purified by an automated high-throughput purification system. A total of 2592 4-amido-pyrrolidinones were ultimately isolated as single diastereomers from a matrix of 1920 syntheses. After the four-step synthesis and HPLC purification, the average yield of a single diastereomer was 36.6%. The average chemical purity was >90%, and the average diastereomeric purity was >87%. The choice of chiral amines used to make amides with heterocyclic acid chlorides had a dramatic effect on success. Analysis of the relationship between amines used for synthesis and the diastereomeric separation showed that amides made from chiral 1,2-amino alcohols gave superior separation to amides from chiral morpholines. The presence of a hydrogen bond donor on the amide side chain seems to be required for a better diastereomeric separation.     

Comparison of the binding stoichiometries of positively charged DNA-binding drugs using positive and negative ion electrospray ionization mass spectrometry

Positive and negative ion electrospray ionization (ESI) mass spectra of complexes of positively charged small molecules (distamycin, Hoechst 33258, [Ru(phen)2dpq]Cl2 and [Ru(phen)2dpqC]Cl2) have been compared. [Ru(phen)2dpq]Cl2 and [Ru(phen)2dpqC]Cl2 bind to DNA by intercalation. Negative ion ESI mass spectra of mixtures of [Ru(phen)2dpq]Cl2 or [Ru(phen)2dpqC]Cl2 with DNA showed ions from DNA-ligand complexes consistent with solution studies. In contrast, only ions from free DNA were present in positive ion ESI mass spectra of mixtures of [Ru(phen)2dpq]Cl2 or [Ru(phen)2dpqC]Cl2 with DNA, highlighting the need for obtaining ESI mass spectra of non-covalent complexes under a range of experimental conditions. Negative ion spectra of mixtures of the minor groove binder Hoechst 33258 with DNA containing a known minor groove binding sequence were dominated by ions from a 1:1 complex. In contrast, in positive ion spectra there were also ions present from a 2:1 (Hoechst 33258: DNA) complex, suggesting an alternative binding mode was possible either in solution or in the gas phase. When Hoechst 33258 was mixed with a DNA sequence lacking a high affinity minor groove binding site, the negative ion ESI mass spectra showed that 1:1 and 2:1 complexes were formed, consistent with existence of binding modes other than minor groove binding. The data presented suggest that comparison of positive and negative ion ESI-MS spectra might provide an insight into various binding modes in both solution and the gas phase.     

A chemical defense mechanism for the nudibranch cadlina luteomarginata

The nudibranch Cadlina luteomarginata from San Diego, California, concentrates selected metabolites from the sponges that constitute its diet. Gut analyses revealed that C. leutomarginata consumes at least ten sponges although Axinella sp. and Myxilla incrustans are most frequently eaten. Field observations and analysis of metabolites suggest that keratose sponges Leiosella idia (=Spongia idia) and Dysidea amblia are also consumed. Three novel compounds, the furan 20, the isonitrile 23 and the isothiocyanate 24 were identified by analysis of spectral data. The secondary metabolites of C. leuteomarginata were found only in the dorsum, which is exposed to potential predators. Five metabolites of C. luteomarginata were screened for antifeedant activity against fish and all showed some activity at 10–100 μ/mg in food pellets.     

Quantification of DNA in forensic samples

Quantification of DNA in a forensic sample is of major importance for proper DNA amplification and STR profiling. Several methods have been developed to quantify DNA, from basic UV spectrometry, through gel-based techniques, to dye staining, blotting techniques, and, very recently, DNA amplification methods (polymerase chain reaction, PCR). Early techniques simply measured total DNA, but newer techniques can specifically measure human DNA while excluding non-human DNA (foodstuff, animal, or bacterial contamination). These newer assays can be faster and less expensive than traditional methods, making them ideal for the busy forensic laboratory. This paper reviews classic and newer quantification techniques and presents methods recently developed by the authors on the basis of PCR of Alu sequences.     

Rearrangement of Langmuir-Blodgett stearic acid films and band assignments in deuterated stearic acid monolayers

Band assignments in the C-D stretching region of straight chain hydrocarbon species are derived from the spectra of stearic acid monolayers on gold. The fatty acid molecules reorient with respect to the metal surface as the films age. Correlating the changes in the IR spectra of both the undeuterated and deuterated acids allows one to identify the vibrational modes of the latter based on the accepted assignments of the former. The CD₂ asymmetric and symmetric stretches are observed at 2194 and 2086 cm^–1, respectively. Bands at 2212 and 2221 cm^–1 are attributed to asymmetric in-plane and out-of-plane CD₃ stretches. Assignments of several other features in this region are given while one band remains unassigned.