Modifying chemotherapy response by targeted inhibition of eukaryotic initiation factor 4A.

Translation is regulated predominantly at the initiation phase by several signal transduction pathways that are often usurped in human cancers, including the PI3K/Akt/mTOR axis. mTOR exerts unique administration over translation by regulating assembly of eukaryotic initiation factor (eIF) 4F, a heterotrimeric complex responsible for recruiting 40S ribosomes (and associated factors) to mRNA 5' cap structures. Hence, there is much interest in targeted therapies that block eIF4F activity to assess the consequences on tumor cell growth and chemotherapy response. We report here that hippuristanol (Hipp), a translation initiation inhibitor that selectively inhibits the eIF4F RNA helicase subunit, eIF4A, resensitizes Eµ-Myc lymphomas to DNA damaging agents, including those that overexpress eIF4E-a modifier of rapamycin responsiveness. As Mcl-1 levels are significantly affected by Hipp, combining its use with the Bcl-2 family inhibitor, ABT-737, leads to a potent synergistic response in triggering cell death in mouse and human lymphoma and leukemia cells. Suppression of eIF4AI using RNA interference also synergized with ABT-737 in murine lymphomas, highlighting eIF4AI as a therapeutic target for modulating tumor cell response to chemotherapy.

Theoretical and experimental determination of the effects governing the transannular Diels-Alder reaction of trans-trans-cis systems with or without activation of the dienophile.

A thorough study of the transannular Diels-Alder (TADA) reaction of trans-trans-cis macrocyclic trienes was carried out. It led to a better understanding of various parameters that govern the TADA reaction in particular and the Diels-Alder reaction in general. Thus, carbonyl activation of the dienophile and substitution of the diene are discussed, as well as the presence of substituents on the macrocycle and their respective effects at the transition-state level.

New approach to aphidicolin and total asymmetric synthesis of unnatural (11R)-(-)-8-epi-11-hydroxyaphidicolin by tandem transannular Diels-Alder/aldol reactions.

The 8-epiaphidicolane skeleton (3) was formed in one key reaction by highly diastereoselective tandem transannular Diels-Alder (TADA)-aldol reactions from the trans-trans-cis trienic macrocycle (4). The unnatural derivative (11R)-(-)-8-epi-11-hydroxyaphidicolin (2) was thus constructed, and an original solution to the C16 functionalization problem of many aphidicolin (1) syntheses is presented.

Increasing the efficiency of the transannular diels-alder strategy via stille macrocyclizations

To increase the potential and flexibility of the transannular Diels-Alder strategy to build tricycles and tetracycles, the synthesis of macrocyclic trienes of defined geometries has been approached via Stille macrocyclization, giving very high yield and purity of the desired macrocycles or tricycles.

Differential reactivity of alpha- and beta-anomers of glycosyl acceptors in glycosylations. A remote consequence of the endo-anomeric effect?

When phenyl tri-O-benzyl-1-thio-beta-D-galactopyranosiduronic acid esters were coupled with a 1/1 mixture of alpha and beta 2,3 di-O-protected D-galactopyranosiduronic acid esters, the beta-anomer proved to be more reactive. Data from theoretical calculations suggested that the enhanced reactivity of this anomer compared with the alpha one would be due to a stronger hydrogen bond of the C-4 OH with the ring oxygen.

Transannular Diels-Alder studies on the asymmetric total synthesis of chatancin: the pyranophane approach.

[reaction: see text] A pathway is proposed for the biosynthesis of (+)-chatancin and (+)-sarcophytin linking these tetracycles to cembranoids by a pyranophane transannular Diels-Alder reaction. Preliminary synthetic results in this direction to reach macrocyclic dienedione 28 from farnesol are reported. Major synthetic steps include a Prins reaction, two enantioselective hydrogenations, and a macrocyclization via a beta-ketosulfoxide Michael-addition on an enone.

Total asymmetric synthesis of the aphidicolin derivative (11R)-(-)-8-epi-11-hydroxyaphidicolin using tandem transannular Diels-Alder/aldol reactions.

[reaction: see text] Aphidicolin unnatural derivative (2) was synthesized using a new tandem transannular Diels-Alder/aldol methodology. The 8-epi-aphidicolane skeleton is constructed in a highly diastereoselective manner and converted into (11R)-(-)-8-epi-11-hydroxyaphidicolin (2). An efficient method for the difficult C16 funtionalization is presented.

Solid phase combinatorial synthesis of a library of macro-heterocycles and related acyclic compounds.

A solid phase synthesis of macrolactones from three building blocks and in eight steps is described. The synthesis which is carried out on the DHP resin includes Mitsunobu and DIC couplings. The macrocyclization occurs by SN2 displacement of an allylic chloride by a malonate anion. The synthetic methodology is suitable for the synthesis of arrays of macrocycles as well as linear compounds.

Progress toward the total synthesis of cassaine via the transannular diels-alder strategy

The transannular Diels-Alder reaction of trans-trans-trans macrocyclic triene A, bearing two cis substiuents in C(12) and C(13) as well as a gem-dimethyl in C(4), was studied. Under thermal conditions, only the desired trans-anti-cis tricycle B was obtained. This tricycle represents an advanced intermediate toward the total synthesis of cassaine C.

Structural components of ryanodine responsible for modulation of sarcoplasmic reticulum calcium channel function.

Comparative molecular field analysis (CoMFA) was used to analyze the relationship between the structure of a group of ryanoids and the modulation of the calcium channel function of the ryanodine receptor. The conductance properties of ryanodine receptors purified from sheep heart were measured using the planar, lipid bilayer technique. The magnitude of the ryanoid-induced fractional conductance was strongly correlated to specific structural loci on the ligand. Briefly, electrostatic effects were more prominent than steric effects. The 10-position of the ryanoid had the greatest influence on fractional conductance. Different regions of the ligand have opposing effects on fractional conductance. For example, steric bulk at the 10-position is correlated with decreased fractional conductance, whereas steric bulk at the 2-position (isopropyl position) is correlated with increased fractional conductance. In contrast to fractional conductance, the 3-position (the pyrrole locus) had the greatest influence on ligand binding, whereas the 10-position had comparatively little influence on binding. Two possible models of ryanodine action, a direct (or channel plug) mechanism and an allosteric mechanism, were examined in light of the CoMFA. Taken together, the data do not appear to be consistent with direct interaction between ryanodine and the translocating ion. The data appear to be more consistent with an allosteric mechanism. It is suggested the ryanoids act by inducing or stabilizing a conformational change in the ryanodine receptor that results in the observed alterations in cation conductance.

Electrophysiological effects of ryanodine derivatives on the sheep cardiac sarcoplasmic reticulum calcium-release channel.

We have examined the effects of a number of derivatives of ryanodine on K+ conduction in the Ca2+ release channel purified from sheep cardiac sarcoplasmic reticulum (SR). In a fashion comparable to that of ryanodine, the addition of nanomolar to micromolar quantities to the cytoplasmic face (the exact amount depending on the derivative) causes the channel to enter a state of reduced conductance that has a high open probability. However, the amplitude of that reduced conductance state varies between the different derivatives. In symmetrical 210 mM K+, ryanodine leads to a conductance state with an amplitude of 56.8 +/- 0.5% of control, ryanodol leads to a level of 69.4 +/- 0.6%, ester A ryanodine modifies to one of 61.5 +/- 1.4%, 9,21-dehydroryanodine to one of 58.3 +/- 0.3%, 9 beta,21beta-epoxyryanodine to one of 56.8 +/- 0.8%, 9-hydroxy-21-azidoryanodine to one of 56.3 +/- 0.4%, 10-pyrroleryanodol to one of 52.2 +/- 1.0%, 3-epiryanodine to one of 42.9 +/- 0.7%, CBZ glycyl ryanodine to one of 29.4 +/- 1.0%, 21-p-nitrobenzoyl-amino-9-hydroxyryanodine to one of 26.1 +/- 0.5%, beta-alanyl ryanodine to one of 14.3 +/- 0.5%, and guanidino-propionyl ryanodine to one of 5.8 +/- 0.1% (chord conductance at +60 mV, +/- SEM). For the majority of the derivatives the effect is irreversible within the lifetime of a single-channel experiment (up to 1 h). However, for four of the derivatives, typified by ryanodol, the effect is reversible, with dwell times in the substate lasting tens of seconds to minutes. The effect caused by ryanodol is dependent on transmembrane voltage, with modification more likely to occur and lasting longer at +60 than at -60 mV holding potential. The addition of concentrations of ryanodol insufficient to cause modification does not lead to an increase in single-channel open probability, such as has been reported for ryanodine. At concentrations of > or = 500 mu M, ryanodine after initial rapid modification of the channel leads to irreversible closure, generally within a minute. In contrast, comparable concentrations of beta-alanyl ryanodine do not cause such a phenomenon after modification, even after prolonged periods of recording (>5 min). The implications of these results for the site(s) of interaction with the channel protein and mechanism of the action of ryanodine are discussed. Changes in the structure of ryanodine can lead to specific changes in the electrophysiological consequences of the interaction of the alkaloid with the sheep cardiac SR Ca2+ release channel.

Structural determinants of high-affinity binding of ryanoids to the vertebrate skeletal muscle ryanodine receptor: a comparative molecular field analysis.

Ryanodine binds to specific membrane proteins, altering the calcium permeability of intracellular membranes. In this study 19 ryanoids were isolated or synthesized and the structures correlated to the strength of binding to vertebrate skeletal muscle ryanodine receptors. Global minima were determined by employment of molecular mechanics and dynamics augmented by systematic searching of conformational space. Overall, steric and electrostatic factors contribute about equally to the differences in the experimentally determined dissociation constants. The dominant electrostatic interaction is localized to a hydroxyl group in an apolar region of the molecule. The pyrrole and isopropyl groups located together at one pole of the molecule have the greatest effect on steric interactions between ligand and receptor. We suggest ryanodine binds to the receptor with the pyrrole and isopropyl groups buried deep inside a cleft in the protein. This arrangement places special importance on the conformation of the pyrrole and isopropyl groups. In contrast, the opposite pole appears to be positioned at the entrance of the binding pocket because bulky adducts placed in the 9 position of ryanodine alter binding minimally. For example, a fluorescent ryanodine adduct was synthesized which has a dissociation constant close to that of ryanodine. Detailed examination reveals subtle interactions between ryanoid and receptor. In many cases, the major factors altering the strength of binding were found to be conformational alterations in the molecule remote from the site of covalent modification.

Functionalized hydrocarbons with condensed ring skeletons. X. A methyltricyclo[7.4.0.0(2,6)]tetradec-7-ene.

(1) 1,9-trans-1,2-cisoid-2,6-cis-4,11,11-Tris(methoxycarbonyl)-6- methyltricyclo[7.4.0.0(2,6)]-tridec-7-ene-4,2-carbolacton e+ ++, C21H26O8, Mr = 406.43, monoclinic, P1, a = 6.0774 (2), b = 12.3784 (5), c = 14.2565 (4) A, alpha = 72.906 (3), beta = 86.361 (3), gamma = 78.181 (3) degrees, V = 1003.38 (6) A3, Dx = 1.345 Mg m-3, Z = 2, lambda (Cu K alpha) = 1.54056 A, mu = 0.82 mm-1, F(000) = 432, room temperature, final R = 0.043 for 2841 observed reflections. The tricyclic compound (1) has the same carbon framework as in the BCD rings in a steroid nucleus. Ring B adopts a chair while ring C has a half-chair conformation. A trans relative stereochemistry is observed at the BC ring junction while a cis hydrinclane is observed for the CD junction, the lactone bridge being cis to the angular methyl group at C(6) and to the hydrogen at C(1).