The impact of polystyrene resins in solid-phase organic synthesis

Summary A major objective of the DIVERSOMER^® technology is to provide pure and characterized compounds for biological testing in order to prevent false negatives in our libraries. On several occasions, analysis of the final products by¹H-NMR and MS, has revealed by-products from the polystyrene solid support. Subsequently, three alternative methods were studied to remove polystyrene by-products; (i) prewashing of the resin prior to execution of the synthesis; (ii) pretreatment of the resin with the cleavage conditions consistent with the solid-phase synthesis reaction scheme; and (iii) parallel purification.     

Structure-activity studies of antitumor agent irofulven (hydroxymethylacylfulvene) and analogues

Many analogues of the antitumor agent irofulven have been readily prepared by replacing the allylic hydroxyl with a variety of nucleophiles. Analogues of acylfulvene (the precursor to irofulven) were also prepared by Michael reaction with acrolein. The toxicity of the analogues was determined, as well as preclinical antitumor activity. Several analogues exhibited good activity in mouse xenografts. Structural requirements for activity are discussed.     

A critical comparison of approximation methods and models for equilibrium properties of low-barrier hydrogen bonds

Recent experimental evidence has led to the conclusion that short, strong hydrogen bonds can stabilize transition states of enzyme catalyzed biochemical reactions. Evidence for such hydrogen bonds is the low value of the isotopic fractionation factor, phi, which is defined as the equilibrium constant for the generic reaction, R-H + DOH <--> R-D + HOH, where H is the hydrogen atom participating in the low-barrier hydrogen bond in a molecule R-H. In this work we assess two approximation methods for computing the isotopic fractionation factors for single and multidimensional systems containing a low-barrier hydrogen bond. These methods are WKB and an approach that corrects the classical partition function via a quantum correction factor. We find that the latter approach is universally accurate and applicable in both single and multidimensional systems containing a low-barrier hydrogen bond. We also assess two different models for the coupling of a molecule's low-barrier hydrogen bond to other degrees of freedom, both internal and external to the molecule, and show that each leads to a lowering of the fractionation factor.     

Greater insight into the MTDSC technique involving fundamental sinusoidal heat flow equations

Summary Modulated temperature DSC was investigated, comparing data found experimentally to that derived from theory. Deviation from theory was found with regard to the amplitude of the modulated heat flow signal when large modulation amplitudes were employed in the experiment. These deviations were determined to be dependent on the absolute temperature and it was concluded that further investigation of the heat flow signal obtained during MTDSC experiments is required.