Grant A. Krafft

DESIGN AND SYNTHESIS OF NEW FLUOROGENIC HIV PROTEASE SUBSTRATES BASED ON RESONANCE ENERGY TRANSFER

Abstract The design and synthesis of new fluorogenic substrate probes for HIV protease based on resonance energy transfer arc described. These substrates permit sensitive, continuous measurement of HIV protease activity.

Generation of thioaldehydes via fluoride induced elimination of α-silyldisulfides

Abstract A mild, efficient and general method for the generation of reactive thioaldehydes from α-silyldisulfides is described.

Actin assembly activity of cytochalasins and cytochalasin analogs assayed using fluorescence photobleaching recovery

The effects on actin self-assembly of 9 common cytochalasins and 9 synthetic analogs have been assayed using fluorescence photobleaching recovery (FPR). The specific assembly activities of cytochalasins determined by this assay are (i) reduction of the fraction of actin molecules incorporated into filaments; (ii) increase of the steady-state diffusion coefficients of filaments, from which filaments shortening may be inferred; and (iii) acceleration of the initial rate of assembly. Of the compounds studied, only cytochalasin D shows strong activity of all three types. The range of activities shown by other compounds indicates clearly that these three activity types are distinct and independent. Inspection of the molecular structures of these 18 compounds for correlation of structure and activity reveals that the three different activities depend on distinct structural features. The Mg2+ dependence of filament-shortening activity by certain cytochalasins may be explained by the Mg2+ chelating ability of two suitably positioned oxygen atoms on the convex face of the bicyclic isoindolone system. Inhibition of filament elongation may involve very specific, high-affinity cytochalasin interactions at a binding site on terminal actin molecules, while accelerating activity may occur by weaker, less specific binding interactions of cytochalasins with monomeric actin.

Regiochemical preferences in selenoaldehyde cycloadditions

Abstract The regiochecnical preferences of substituted selenoaldehydes in cycloaddition reactions with electronically biased dienes have been examined. Selenoaldehydes substituted with electron withdrawing groups exhibit “ortho-para” orientation, while selenoaldehydes substituted with donating or conjugating groups exhibit “meta” orientation. Nitrile oxide dipolar cycloadditions of selenoformaldehyde and selenobenzaldehyde are also described.

Photoactivable fluorophores. 2. Synthesis and photoactivation of functionalized 3-aroyl-2-(2-furyl)-chromones.

Abstract The synthesis and photochemistry of functionalized 3-aroyl-2-(2-furyl)-chromones 1 which are photoactivable fluorophores are described. Irradiation converts the non-fluorescent furyl chromones to highly fluorescent 1-arylfuro[3,4b]chromones 3 . Functionality has been incorporated to permit covalent attachment, impart aqueous solubility and to maximize the fluorescence of the ultimate 1-arylfuro[3,4b]chromone fluorophore. An efficient synthetic pathway to the furyl chromones via an intramolecular Dieckman cyclization also is described.

Photoactivable fluorophores. 1. Synthesis and photoactivation ofo-nitrobenzyl-quenched fluorescent carbamates.

Abstract The synthesis and photoactivation of a new type of fluorescent probe, the photoactivable fluorophore (PAF) are described. The PAFs described in this paper consist of fluorescent aromatic amines coupled to substituted nitrobenzyl quenching chromophores via a carbamate linkage. Photoactivation occurs by an intramolecular photo-redox reaction, converting the o-nitrobenzyl group to a labile o -nitrosobenzaldehyde hemiacetal which fragments with loss of CO 2 to liberate the fluorescent amine. Photoactivation quantum yields also are reported.

Selenofluorenone: Synthesis and cycloaddition chemistry

Abstract Selenofluorenone, prepared from fluorenyl selenocyanate by base-induced elimination, participates efficiently in Diels-Alder cycloaddition and 1,3-dipolar cycloaddition reactions.

Functionalization of furans via phenacyl sulfides

Abstract A mild, efficient, photochemical method for the functionalization of furans via phenacyl sulfides is described.

Fluorescence Photoactivation and Dissipation (FPD)

Fluorescence methods have emerged as indispensable analytical and tracer techniques for a diverse range of biochemical, biophysical and physical studies that depend upon highly sensitive measurements of physical environment. This emergence has been hastened by advances in low-level light detection and by the development of coherent, variable-wavelength, and polarized excitation sources. Moreover, the spectrum of biological and physical applications of fluorescence methods has been expanded broadly by the development and availability of fluorescent molecules with specifically tailored characteristics. The attachment of these fluorescent molecules to molecular species has become a powerful approach for investigating the structure and dynamics of complex systems.

Stereospecific displacement of sulfur from chiral centers. Activation via thiaphosphonium salts

Abstract The first general method for direct displacement of sulfur from chiral carbon centers has been developed. Chiral mercaptans are readily converted to the corresponding thiaphosphonium salts by treatment with t-butyl hypochlorite and hexamethylphosphorous triamide. Metathesis with ammonium hexafluorophosphate provides stable, isolable, crystalline salts which undergo clean nucleophilic diplacement with a variety of heteroatom and carbon based nucleophiles, affording products in which the stereochemistry has been inverted.