Barry M. Goldstein

Cofactor mimics as selective inhibitors of NAD-dependent inosine monophospate dehydrogenase (IMPDH) - The major therapeutic target

IMP dehydrogenase, the key enzyme in de novo synthesis of purine nucleotides, is an important therapeutic target. Three inhibitors of IMP dehydrogenase reached the market; ribavirin (Rebetol) a broad-spectrum antiviral agent, which in combination with interferon-alpha is now used for treatment of hepatitis C virus infections, mizoribine (Bredinin) and mycophenolic mofetil (CellCept) have been introduced as immunosuppressants. Numerous novel inhibitors are under development. This review describes recent progress in the development of new drugs based on inhibition of IMP dehydrogenase.

A database study of nonbonded intramolecular sulfur-nucleophile contacts.

A search of the Cambridge Structural Database (1991, version 4.5) was performed to investigate nonbonded intramolecular 1,4 S...O close contacts of the kind seen in the thiazole nucleoside tiazofurin and other classes of compounds. The search yielded 362 structures with 1,4 S...O connectivity. S...O distances in 70% of these structures were less than the sum of the sulfur and oxygen van der Waals radii. Findings indicate that 1,4 S...O close contacts are common and so probably result from intramolecular interactions rather than from external crystal packing forces. A structure containing a sulfur atom in a conjugated ring system is more likely to exhibit 1,4 S...O close contacts than a structure containing a sulfur atom in an unconjugated and/or acyclic environment. Sulfur-nitrogen contacts were also investigated and were found to show similar properties. These results are consistent with findings from previous quantum-chemical-based studies performed on model fragments [Burling & Goldstein (1992). J. Am. Chem. Soc. 114, 2313-2320].

The chemistry of nicotinamide adenine dinucleotide (NAD) analogues containing C-nucleosides related to nicotinamide riboside.

Oncolytic C-nucleosides, tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide) and benzamide riboside (3-beta-D-ribofuranosylbenzamide) are converted in cell into active metabolites thiazole-4-carboxamide- and benzamide adenine dinucleotide, TAD and BAD, respectively. TAD and BAD as NAD analogues were found to bind at the nicotinamide adenine dinucleotide (cofactor NAD) site of inosine monophosphate dehydrogenase (IMPDH), an important target in cancer treatment. The synthesis and evaluation of anticancer activity of a number of C-nucleosides related to tiazofurin and nicotinamide riboside then followed and are reviewed herein. Interestingly, pyridine C-nucleosides (such as C-nicotinamide riboside) are not metabolized into the corresponding NAD analogues in cell. Their conversion by chemical methods is described. As dinucleotides these compounds show inhibition of IMPDH in low micromolar level. Also, the synthesis of BAD in metabolically stable bis(phosphonate) form is discussed indicating the usefulness of such preformed inhibitors in drug development. Among tiazofurin analogues, Franchetti and Grifantini found, that the replacement of the sulfur by oxygen (as in oxazafurin) but not the removal of nitrogen (tiophenfurin) of the thiazole ring resulted in inactive compounds. The anti cancer activity of their synthetic dinucleotide analogues indicate that inactive compounds are not only poorly metabolized in cell but also are weak inhibitors of IMPDH as dinucleotides.

Benign synthesis of 2-ethylhexanoic acid by cytochrome P450cam: enzymatic, crystallographic, and theoretical studies.

This study examines the ability of P450cam to catalyze the formation of 2-ethylhexanoic acid from 2-ethylhexanol relative to its activity on the natural substrate camphor. As is the case for camphor, the P450cam exhibits stereoselectivity for binding (R)- and (S)-2-ethylhexanol. Kinetic studies indicate (R)-2-ethylhexanoic acid is produced 3.5 times as fast as the (S)-enantiomer. In a racemic mixture of 2-ethylhexanol, P450cam produces 50% more (R)-2-ethylhexanoic acid than (S)-2-ethylhexanoic acid. The reason for stereoselective 2-ethylhexanoic acid production is seen in regioselectivity assays, where (R)-2-ethylhexanoic acid comprises 50% of total products while (S)-2-ethylhexanoic acid comprises only 13%. (R)- and (S)-2-ethylhexanol exhibit similar characteristics with respect to the amount of oxygen and reducing equivalents consumed, however, with (S)-2-ethylhexanol turnover producing more water than the (R)-enantiomer. Crystallographic studies of P450cam with (R)- or (S)-2-ethylhexanoic acid suggest that the (R)-enantiomer binds in a more ordered state. These results indicate that wild-type P450cam displays stereoselectivity toward 2-ethylhexanoic acid synthesis, providing a platform for rational active site design.

Metastable and equilibrium phases in dilute V-N alloys

Alloys of vanadium containing 0 to 10 at. pct nitrogen were prepared and aged at temperatures from 300 to 950°C. The nitrogen solvus line was determined and the discontinuities are discussed in terms of the phases coexisting with the α-phase at various temperatures. Aging temperatures greater than 550°C produced only V3N in equilibrium with the α-phase. Aging at 550°C and below resulted in a sequence of transformations beginning with the precipitation of V16N from supersaturated α-phase. This transformation was followed by the decomposition of the V16N into two other metastable phases, termed VxN and VγN. Longer aging times at 550°C resulted in dissolution of VγN and resultant large discs of V*N precipitate. Further aging yielded V3N. Except for the α-phase, the phases involved in this sequence have nitrogen atoms which are ordered. The crystal structures of both the vanadium atoms and the nitrogen atoms in VxN and VγN are presented and discussed. VN is shown to be bet while VγN is bcc with respect to the vanadium atoms. The morphology of the precipitates is described and discussed in terms of their crystal structures.

Disposition of catecholamines in cardiovascular tissues of aorta coarcted hypertensive rats

Aorta-coarcted hypertensive rats and sham-operated normotensive rats were compared in order to assess the contribution of sympathetic nervous system activity to the elevated blood pressure in these rats at an early (6 days) and chronic (42 days) stage of hypertension. Norepinephrine (NE), epinephrine (E) and dopamine (DA) levels were quantitated in plasma, heart and vascular tissues (aorta, inferior vena cava, mesenteric artery and vein) using a radioenzymatic procedure. Body weight was significantly reduced and mean arterial blood pressure (MABP) significantly increased in the coarcted rats at both stages of hypertension. Plasma catecholamines did not differ at either stage of hypertension. The NE content of the heart and mesenteric artery was significantly decreased in the coarcted rats at both stages of hypertension but unchanged in the other vessels studied. E and DA levels in the heart and all vasculature analyzed remained unaltered at both stages of hypertension. The present results suggest that neither E nor DA makes a major contribution to the development and maintenance of hypertension in the aorta-coarcted rat. The observation of the reduced cardiac NE concentration in the coarcted rats together with literature reports of similar observations in other animal models of hypertension suggests that myocardial NE depletion is a common feature of the hypertension and not dependent on the methodology used to produce that hypertension.

Physiologic determinants of primary impressions for complete dentures

A technique has been described whereby a physiologic registration of the attached and unattached tissues of the denture-bearing areas can be attained. A low-fusing impression wax in conjunction with modeling compound is used for this purpose.

Synthesis and Cytotoxic Activity of Selenophenfurin, a New Inhibitor of IMP Dehydrogenase

Abstract The synthesis of 5-β-D-ribofuranosylselenophene-3-carboxamide (selenophenfurin) is reported. Selenophenfurin was found active as cytotoxic agent and as inosine monophosphate dehydrogenase inhibitor.

Structure-activity relationships of tiazofurin analogs: synthesis and computational studies of 4'-thio derivatives of thiophenfurin and furanfurin

Abstract The synthesis and computational studies of 5-(4-thio-β-D-ribofuranosyl)-furan-3-carboxamide (furanthiofurin) and 5-(4-thio-β-D-ribofuranosyl)thiophene-3-carboxamide (thiophenthiofurin) are reported.

Coupling of MBP fusion protein cleavage with sparse matrix crystallization screens to overcome problematic protein solubility

Crystal Clear Sparse matrices are a familiar tool to anyone who has set about seeking diffraction-quality crystals for X-ray crystallography studies. These multiwell plates provide an efficient way to screen multitudinous conditions for that just-right environment in which crystals can form. Jumping to a sparse matrix screen during one of the first steps of recombinant protein production might seem like muddled thinking, but Gruswitz et al. describe the method to the madness in a Benchmark beginning on p. 476. The authors first explain that maltose binding protein (MBP) is frequently used as a fusion tag to improve protein solubility, but since it usually must be removed before structural analysis, cleavage can often cruelly send the protein back to its original insoluble state. Gruswitz et al. therefore recommend performing the proteolytic removal of MBP in a sparse matrix setup, thus allowing for efficient screening of conditions in which the liberated polypeptide is soluble. Eight hours after preparing...