No abstract

High-level ab initio calculations have been used to determine the minimum energy structures of N,N‘-diformylhydrazine, N-methyl-N,N‘-diformylhydrazine, and N,N‘-dimethyl-N,N‘-diformylhydrazine. These calculations show that the global minimum is a nonplanar structure in which the nitrogen lone pairs are essentially perpendicular to one another. However, the energy required for (Z,Z)-diformylhydrazine to adopt a planar structure is less than 1 kcal/mol (MP2/6-31+G**). This is due to attractive intramolecular hydrogen bonds between the N-hydrogens and the carbonyl oxygens in the planar geometry. When one or both amide configurations are inverted (Z,E; E,E), or when the nitrogens are substituted, with methyl for example, these hydrogen bonds are lost and the planar structure becomes much less stable relative to the twisted rotamer. Thus, we conclude from these calculations that diacylhydrazines are intrinsically nonplanar with respect to the CO−N−N−CO torsion, and that with the exception of (Z,Z)-diformylhydrazine the rotational barriers are large. The observation of a planar crystal structure for diformylhydrazine is due to additional intermolecular hydrogen bonds which are available to planar diformylhydrazine in the crystal lattice. Finally, these calculations have significant implications for the structure and dynamical properties of nonsteroidal ecdysone agonists, azapeptides, and azatides which incorporate the diacylhydrazine structure.

The ecdysteroid-responsive Drosophila melanogaster B(II) cell line is a prototypical homologous inducible gene expression system. A training set of 71 ecdysteroids, for which the -log(EC(50)) potencies in the ecdysteroid-responsive B(II) cell line were measured, was used to construct 4D-QSAR models. Four nearly equivalent optimum 4D-QSAR models, for two modestly different alignments, were identified (Q(2) = 0.76-0.80). These four models, together with two CoMFA models, were used in consensus modeling to arrive at a three-dimensional pharmacophore. The C-2 and C-22 hydroxyls are identified as hydrogen-bond acceptor sites which enhance activity. A hydrophobic site near C-12 is consistent with increasing activity. The side-chain substituents at C-17 are predicted to adopt semiextended "active" conformations which could fit into a cylinder-shaped binding pocket lined largely with nonpolar residues for enhanced activity. A test set of 20 ecdysteroids was used to evaluate the QSAR models. Two 4D-QSAR models for one alignment were identified to be superior to the others based on having the smallest average residuals of prediction for the prediction set (0.69 and 1.13 -log[EC(50)] units). The correlation coefficients of the optimum 4D-QSAR models (R(2) = 0.87 and 0.88) are nearly the same as those of the best CoMFA model (R(2) = 0.92) determined for the same training set. However, the cross-validation correlation coefficient of the CoMFA model is less significant (Q(2) = 0.59) than those of the 4D-QSAR models (Q(2) = 0.80 and 0.80).

The ecdysteroid agonist activity of 71 HPLC-purified ecdysteroids was measured in the Drosophila melanogaster BII tumorous blood cell line assay. The resultant log(ED50) values, spanning almost 6 orders of magnitude, were used to construct a comparative molecular field analysis (CoMFA) model in which conformations were selected by homology to the crystal structure of ecdysone. Model A was constructed by utilization of the region-focused electrostatic indicator field (q2 = 0.631, r2 = 0.903, 5 components, 4 outliers). Model B made use of region-focused electrostatic and steric indicator fields along with MlogP (q2 = 0.694, r2 = 0.892, 5 components, 4 outliers). The model and its underlying bioassay data support a pharmacophore hypothesis in which ecdysteroid binding is understood to be due principally to the summation of localized interactions from approximately six specific loci. This is in contrast to previous structure-activity relationship hypotheses which are formulated in terms of the presence or absence of essential functional groups, without which ecdysteroid receptor affinity would be completely absent. The present CoMFA model is utilized to predict the activities of heretofore unknown ecdysteroids.