Design and synthesis of a dimeric derivative of RK-682 with increased inhibitory activity against VHR, a dual-specificity ERK phosphatase: implications for the molecular mechanism of the inhibition.

BACKGROUND: VHR is a dual-specificity phosphatase, which dephosphorylates activated ERK1/2 and weakens the ERK signaling cascade in mammalian cells. A selective inhibitor is expected to be useful for revealing the physiological function of VHR. RESULTS: First, we investigated the molecular mechanism of VHR inhibition by a known natural product, RK-682. Kinetic analysis indicated that inhibition was competitive toward the substrate, and two molecules of RK-682 were required to inhibit one molecule of VHR. Based on the structure-activity relationships for VHR inhibition by RK-682 derivatives, we constructed a binding model using molecular dynamics calculation. Based on this model, we designed and synthesized a novel dimeric derivative. As expected, the dimeric derivative showed increased inhibition of VHR, supporting our proposed mechanism of VHR inhibition by RK-682. CONCLUSION: We have developed a novel inhibitor of VHR based on the results of kinetic analysis and docking simulation.

DNA binding by an amino acid residue in the C-terminal half of the Rel homology region.

BACKGROUND: Members of the Rel family of transcription factors are important in regulating the inflammatory, acute phase, and immune responses in mammals. The structural basis for sequence-specific binding by Rel proteins is poorly understood, however. In the studies reported here, a new photoaffinity labeling procedure has been used to probe DNA contacts established by a Rel protein, the p50 homodimer of NF-kappa B. RESULTS: Using a novel post-synthetic modification method, 8-azido-2'-deoxyadenosine (N3dA), a photoactive analog of 2'-deoxyadenosine, was introduced at a specific site within a consensus DNA binding site for the NF-kappa B p50 homodimer. Upon irradiation with ultraviolet light, the N3dA-substituted DNA was efficiently photocrosslinked to p50. The crosslinked amino acid of p50 was identified as K244, which lies in the carboxy-terminal half of the Rel homology region (RHR). Mutation of K244 exerts strong effects on DNA binding, confirming the importance of this residue for p50-DNA interactions. CONCLUSIONS: We have used N3dA-containing DNA to identify a residue of NF-kappa B p50 that contacts DNA illustrating the value of this approach in studies of protein-DNA interactions. K244 appears not to contact a DNA base, but rather a phosphate moiety that lies nearby. The segment of protein sequence in which K244 resides has been implicated in dimerization. The results presented here suggest that the DNA-binding domain extends farther toward the carboxy-terminus than previously thought.

Synthesis of a tetronic acid library focused on inhibitors of tyrosine and dual-specificity protein phosphatases and its evaluation regarding VHR and cdc25B inhibition.

Selective inhibitors of protein tyrosine phosphatases (PTPs) and dual-specificity phosphatases (DSPs) are expected to be useful tools for clarifying the biological functions of the PTPs themselves and also to be candidates for novel therapeutics. We planned a library approach for the identification of PTP/DSP inhibitors in which 3-acyltetronic acid is used as a "core" phosphate mimic. A series of novel tetronic acid derivatives were synthesized and evaluated as inhibitors of the dual-specificity protein phosphatases VHR and cdc25B. Several compounds are found to be potent inhibitors of cdc25B, which is a key enzyme for cell-cycle progression. The promising results described herein strongly indicated that this tetronic acid library is potent as a library focused on the PTP/DSP-selective inhibitor.

[Development of highly selective synthetic methods utilizing arenetricarbonylchromium complexes and their application to syntheses of therapeutic agents].

The development of new methodologies for the stereocontrolled synthesis of complex molecules is very important for the efficient synthesis of therapeutic agents. In this review, 1) the stereocontrolled synthesis of exocyclic olefins using arene.Cr(CO)3-catalyzed 1,4-hydrogenation of conjugated diene and its application to the synthesis of prostacyclin analogs, 2) new catalytic activities of arene.Cr(CO)3 as a hydrogenation catalyst, 3) the stereocontrolled synthesis of silyl dienol ethers and dienamides using arene.Cr(CO)3-catalyzed isomerization, and 4) a novel carbon-carbon bond-forming reaction through eta 5-pentadienylchromium complexes, are described.

Polymer-bound N-hydroxysuccinimide esters: a column-free fluorescent-labeling method.

Polymer-bound N-hydroxysuccinimide esters of 1-pyrenebutyric acid, 6-carboxyfluorescein diacetate, and biotin were efficiently prepared. Column-free fluorescent- and biotin-labeling reactions of various amines using these resins were successfully demonstrated.

Photoaffinity labeling of PKC isozymes by phorbol ester derivatives.

Photoaffinity probes PPDA and PPTD, which have diazoacetyl and trifluorodiazopropionyl group at C-13 position in phorbol, respectively, were synthesized. Photoaffinity labeling of protein kinase C isozymes by both the probes resulted in specific cross-linking.

Stereocontrolled synthesis of exocyclic olefins using arene tricarbonyl chromium complex-catalyzed hydrogenation. I. Efficient synthesis of carbacyclin and its analogs.

An efficient synthesis of carbacyclin and its analogs (2-7) is described in which the stereospecific 1,4-hydrogenation of a 1,3-diene to an internal monoene plays a key role. That is, arene.Cr(CO)3 complex-catalyzed 1,4-hydrogenation of the dienes 13 and 58, obtainable from the Corey lactone in good yields, under high H2 pressure afforded the exocyclic olefins 14 and 61 stereospecifically in excellent yields, and these intermediates were converted to therapeutically useful carbacyclin (2) and its analogs 3-7 in a usual way.

Alpha-glucosidase inhibitors with a phthalimide skeleton: structure-activity relationship study.

Alpha-glucosidase inhibitors with a phthalimide skeleton were prepared. Structure-activity relationship studies indicated a critical role for the hydrophobicity of the substituent at the nitrogen atom of the phthalimide skeleton. Introduction of electron-withdrawing groups, including a nitro group and chlorine, influenced the activity. Optimization studies led us to design 4,5,6,7-tetrachloro-N-phenylphthalimide (CPOP) and its N-phenylalkyl derivatives. CP0P and 4,5,6,7-tetrachloro-N-(4-phenylbutyl)phthalimide (CP4P) proved to be more potent alpha-glucosidase inhibitors than the known inhibitor 1-deoxynojirimycin.

Novel phorbol analogs which bind to protein kinase C (PKC) without activation.

13-Deacetoxy-11-demethyl-phorbol derivatives with acyl groups of various lengths (from hexanoyl to tetradecanoyl) at the C-12 position were synthesized in an optically active form. Although considerable binding affinities to PKC were observed by analogs 3-7, no activation of PKC was seen even at 10 microM.

Structure of the NF-kappa B p50 homodimer bound to DNA.

The structure of a large fragment of the p50 subunit of the human transcription factor NF-kappa B, bound as a homodimer to DNA, reveals that the Rel-homology region has two beta-barrel domains that grip DNA in the major groove. Both domains contact the DNA backbone. The amino-terminal specificity domain contains a recognition loop that interacts with DNA bases; the carboxy-terminal dimerization domain bears the site of I-kappa B interaction. The folds of these domains are related to immunoglobulin-like modules. The amino-terminal domain also resembles the core domain of p53.

Evidence for a non-alpha-helical DNA-binding motif in the Rel homology region.

The Rel family of transcription factors serve as terminal messengers in a variety of developmental and receptor-mediated signaling pathways. These proteins are related by a domain of approximately 280 amino acids, the Rel homology region, which mediates dimerization and sequence-specific binding to DNA. Here we report the use of photocrosslinking and site-directed mutagenesis to identify specific contact partners in a Rel protein-DNA interface. Within the Rel homology region of NF-kappa B p50 (also known as KBF1), two amino acid residues were identified by photocrosslinking to adjacent bases in a beta-interferon regulatory element. Secondary structure analysis suggests that the DNA-binding motif of the Rel homology region comprises a beta-turn-beta structure, in contrast to the alpha-helical motifs so commonly observed in transcription factors.

Novel alpha-glucosidase inhibitors with a tetrachlorophthalimide skeleton.

Novel alpha-glucosidase inhibitors with a tetrachlorophthalimide skeleton were prepared and their structure-activity relationships were analyzed. Among them, N-phenyl-4,5,6,7-tetrachlorophthalimide (CPOP: 2) and N-(4-phenylbutyl)-4,5,6,7-tetrachlorophthalimide (CP4P: 6) showed very potent inhibitory activity, being more potent than 1-deoxynojirimycin (dNM: 1). Mechanistic studies revealed that CPOP (2) and CP4P (6) inhibit alpha-glucosidase non-competitively and competitively, respectively.

Asymmetric synthesis of a 3-acyltetronic acid derivative, RK-682, and formation of its calcium salt during silica gel column chromatography.

RK-682 was reported to be a potent protein tyrosine phosphatase inhibitor. We found that (R)-3-hexadecanoyl-5-hydroxymethyltetronic acid (1) was easily converted to its calcium salt during column chromatography on Silica gel 60, and this calcium salt was identical to RK-682 originally isolated from a natural source. Here we report details of the asymmetric synthesis of (R)-1 and its conversion to the calcium salt. Fast atom bombardment mass spectrometric (FAB-MS) analysis of the free and calcium salt forms of RK-682 is also reported.

Anti-androgenic activity of substituted azo- and azoxy-benzene derivatives.

Substituted phenylazo and phenylazoxy compounds were systematically prepared and their anti-androgenic activity was measured in terms of (1) the growth-inhibiting effect on an androgen-dependent cell line, SC-3, and (2) the binding affinity to nuclear androgen receptor. Generally, azo/azoxy compounds showed cell toxicity, and the growth-inhibiting effects on SC-3 cells correlated with the toxicity. However, some compounds, including 4,4'-dinitroazobenzene (25), 4,4'-dimethoxyazobenzene (33), and 2,2'-dichloroazoxybenzene (47), possessed potent anti-androgenic activity without apparent cell toxicity.

(2E,6R)-8-hydroxy-2,6-dimethyl-2-octenoic acid, a novel anti-osteoporotic monoterpene, isolated from Cistanche salsa.

(2E,6R)-8-Hydroxy-2,6-dimethyl-2-octenoic acid [(R)-HDOA], a novel monoterpene from Cistanche salsa, a Chinese herb, was found to be an anti-osteoporotic compound. The extract of Cistanche salsa significantly suppressed the bone weight loss in ovariectomized mice, a postmenopausal osteoporosis model. The active substance was then purified by using this osteoporotic model and the chemical structure was determined. The active compound from Cistanche salsa, (R)-HDOA, suppressed the decrease of bone weight and the mechanical strength in the ovariectomized mice. Furthermore, (R)- and (S)-HDOA were synthesized and the activity of each was evaluated. (R)-HDOA suppressed the bone weight loss, although (S)-HDOA did not showed any activity.

Identification of protein disulfide isomerase as a phorbol ester-binding protein.

A specific binding protein for 12-O-tetradecanoylphorbol 13-acetate (TPA), different from protein kinase C (PKC) and histone H1, was purified from HeLa cell extract by the use of affinity gel pendanted with phorbol ester (TPA-GEL). The purified binding protein was identified as protein disulfide isomerase (PDI, EC 5.4.3.1) by peptide sequence analysis. The dissociation constants (Kd's) of TPA to PDI, histone H1 and PKCalpha were determined to be 1.03 x 10(-6) M, 5.70 x 10(-7) M, and 4.00 x 10(-7) m, respectively, by the surface plasmon resonance (SPR) method. TPA moderately inhibited PDI activity assessed in terms of reactivation of denatured RNase A.