Nicholas A. Boyle

Peptidomimetics and Peptide Backbone Modifications

The replacement of the amide bond in a peptide backbone is a widely used form of peptide mimicry. Several of the most common amide bond surrogates, including peptidomimetic work done in this laboratory, and their biological applications are presented in this review.

Acute Toxicity Screening of Novel AChE Inhibitors Using Neuronal Networks on Microelectrode Arrays

Spontaneously active neuronal networks grown from embryonic murine frontal cortex on substrate integrated electrode arrays with 64 recording sites were used to assess acute neurobiological and toxic effects of a series of seven symmetrical, bifunctional alkylene-linked bis-thiocarbonate compounds designed to possess anticholinesterase activity. Acute functional neurotoxicity in the absence of cytotoxicity was defined as total collapse of spontaneous activity. All of the compounds were characterized as mixed inhibitors of AChE, with K(i)s in the 10(-7)-10(-6) M range. The neuronal network assays revealed high repeatability for each compound, but surprisingly diverse effects among these closely related compounds. Six of the seven compounds produced changes in network activity at concentrations of 10-350 microM. Three of the compounds were excitatory, two were biphasic (excitatory at lower concentrations, inhibitory at higher), and one was solely inhibitory. Two of the inhibitory compounds produced irreversible inhibition of activity. Responses of cortical cultures to eserine were compared to the effects produced by the test compounds, with only one of seven providing a close match to the eserine profile. Matching of response patterns allows the classification of new drugs according to their response similarity to well-characterized agents. Spontaneously active neuronal networks reflect the interactions of multiple neurotransmitter and receptor systems, and can reveal unexpected side effects due to secondary binding. Utilizing such networks holds the promise of greater research efficiency through a more rapid recognition of physiological tissue responses.

A new synthesis of difluoromethanesulfonamides--a novel pharmacophore for carbonic anhydrase inhibition.

Preparation of the key intermediate carboxydifluoromethanesulfonamide provides direct synthetic access to a wide range of novel difluoromethanesulfonamides, including the acetazolamide analogue (2-ethanoylamino-1,3,4-thiadiazol-5-yl)-difluoromethanesulfonamide. Their water solubility and stability, ether partition coefficient, pK(a) and submicromolar dissociation constants for human carbonic anhydrase isozyme II (HCA II) make them promising candidates for topical glaucoma therapy.

2′,3′-Dideoxynucleoside 5′-β,γ-(Difluoromethylene) Triphosphates With α-P-Thio or α-P-Seleno Modifications: Synthesis and Their Inhibition of HIV-1 Reverse Transcriptase

Nucleoside reverse transcriptase inhibitors (NRTIs) are prodrugs which require three intracellular phosphorylation steps to yield their corresponding, biologically active, nucleoside triphosphate. In order to circumvent this often inefficient phosphorylation cascade, a plausible approach is to provide the active species directly in the form of a stabilized nucleoside triphosphate mimic. We have previously shown that such a mimic, namely 5′-α-R p -borano-β,γ-(difluoromethylene) triphosphate (5′-αBCF 2 TP) is a generic triphosphate mimic that is biologically stable and can render antiviral ddNs with potent inhibitory activity against HIV-1 RT.[1] [2] Herein we report the synthesis and activity against HIV-1 RT of several ddN 5′-α-modified-β,γ-(difluoromethylene) triphosphate mimics with either a non-bridging α-P-thio (5′-αSCF 2 TP) or α-P-seleno (5′-αSeCF 2 TP) modification. One compound, namely, AZT-5′-α-P-seleno-β,γ-(difluoromethylene) triphosphate (diastereomer I), was identified as a potent inhibitor of HIV-1 RT (K i = 64 nM) and represents the first report of HIV-1 RT inhibition data for a nucleotide bearing an α-P-seleno modification. These triphosphate mimics may be useful in the investigation of enzyme mechanism and may have interesting properties with respect to drug resistance and polymerase selectivity.