Tachyphylactic properties of angiotensin II analogs with bulky and hydrophobic substituents at the N-terminus.

Tachyphylaxis, defined as the acute loss of response of some smooth muscles upon repeated stimulations with angiotensin II (Ang II), has been shown to be dependent mainly on the N-terminal region of the ligand. To further study the structural requirements for the induction of tachyphylaxis we have synthesized Ang II analogs containing the bulky and very lipophilic substituents 9-fluorenylmethyloxycarbonyl (Fmoc) and 9-fluorenylmethyl ester (OFm) at the alpha-amino (Nalpha-Fmoc-Ang II) or the beta-carboxyl ([Asp(OFm)1]-Ang II) groups of the Asp1 residue, respectively. In binding assays with Chinese hamster ovary cells transfected with the AT1 Ang II receptor, Nalpha-Fmoc-Ang II bound with high affinity, whereas [Asp(OFm)1]-Ang II showed lower affinity. In biological assays, these two analogs were full agonists and showed 30 and 3%, respectively, of the Ang II potency in contracting the guinea-pig ileum smooth muscle. The two analogs induced tachyphylaxis, in spite of the lack of a free amino group in Nalpha-Fmoc-Ang II. Thus, analogs with Fmoc- or OFm-type groups coupled to the Asp1 residue, whether at the amino or carboxyl functions, induce tachyphylaxis through an unreported mechanism. Based in these findings and those available from the literature, an alternate molecular interaction mode between Ang II N-terminal portion and the AT1 receptor is proposed to explain the tachyphylactic phenomenon.     

Oligonucleotides containing pyrazolo[3,4-d]pyrimidines: 8-Aza-7-deazaadenines with bulky substituents in the 2- or 7-position

The synthesis of the 2'-deoxyadenosine analogues 1b, 2b, and 3c modified at the 7- and/or 2-position is described. The effect of 7-chloro and 2-methylthio groups on the duplex stability is evaluated. For that, the nucleosides 1b, 2b, and 3c were converted to the corresponding phosphoramidites 15, 19, and 22, which were employed in the solid-phase oligonucleotide synthesis. In oligonucleotide duplexes, compound 1b forms stable base pairs with dT, of which the separated 1b-dT base pairs contribute stronger than that of the consecutive base pairs. Compound 2b shows universal base pairing properties while its N8 isomer 3c forms duplexes with lower stability.     

Effect of substituents at the 9-position on cytokinin activity

The preparation and properties of cytokinins substituted in the 9-position by methoxymethyl, propyl and cyclohexyl are described. Each is less active in the soybean and tobacco tests than the unsubstituted cytokinin from which they were derived.     

Asymmetric carbon-carbon bond-forming reaction at the 2-position of a piperidine skeleton

An asymmetric carbon-carbon bond-forming reaction at the 2-position of a piperidine skeleton was exploited. This method consisted of a reaction between 1-(4-methoxybenzoyl)-3,4-didehydro-2-methoxypiperidines and dimethyl malonate catalyzed by Cu(II)-chiral 2,2'-isopropylidenebis(4-phenyl-2-oxazoline) to afford a 2-substituted piperidine skeleton with moderate enantioselectivity.     

Synthesis and antibacterial activity of novel oxazolidinones with methylene oxygen- and methylene sulfur-linked substituents at C5-position

Novel oxazolidinone derivatives of the lead compound RBx 8700, containing methylene oxygen- and methylene sulfur-linked substituents at the C5-position, were synthesized. Antibacterial screening of these compounds against a panel of resistant and susceptible Gram-positive and fastidious Gram-negative bacteria gave compounds 2 and 4 as new antibacterial agents.     

The reaction of trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene with DNA involves attack at the N7-position of guanine moieties

The reaction of trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene (anti-BPDE) with DNA prelabelled with [14C] and [3H]-purine precursors has indicated that in addition to the N2-position of guanine previously reported [10--12] reaction also involves the N7-position of guanine. The hydrocarbon-N7-guanine product was not detected earlier because it is lost from the DNA very readily at pH 7. The same N7-product was obtained by reaction of anti-BPDE with guanine in dimethylformamide.     

Design,synthesis and evaluation of retinoids with novel bulky hydrophobic partial structures

Many synthetic retinoids contain an aromatic structure with a bulky hydrophobic fragment. In order to obtain retinoids with therapeutic potential that do not bind to or activate retinoic acid X receptors (RXRs), we focused on the introduction of novel hydrophobic moieties, that is, metacyclophane, phenalene and benzoheptalene derivatives. The designed compounds were synthesized and their agonistic activities towards RARs and RXRs were evaluated. Most of the active compounds showed selectivity for RARα and RARβ over RARγ, and higher RARβ transactivating activity seemed to correlate with higher cell differentiation-inducing activity towards promyelocytic leukemia cell line HL-60. These compounds showed no agonistic activity towards RXRs.     

Synthesis and insecticidal activity of N-oxydihydropyrroles: 4-hydroxy-3-mesityl-5,5-dimethyl derivatives with various substituents at the 1-position

A new series of N-oxydihydropyrrole derivatives was synthesized and evaluated for insecticidal activity against Nilaparvata lugens and Myzus persicae. Various substituents were introduced to the 1-position of the dihydropyrrole ring, and the derivatives obtained exhibited systemic and/or contact insecticidal activity. The structure-activity relationship revealed that small alkyoxy and alkoxyalkoxy groups were more favorable than alkylcarbonyloxy, alkoxycarbonyloxy, or sulfonyloxy groups as substituents at the 1-position.     

The in vitro and in vivo reaction at the N7-position of guanine of the ultimate carcinogen derived from benzolalpyrene.

The previously reported reaction at N2- and N7- of guanine following addition of 7 alpha,8 beta-dihydroxy-9 beta, 10 beta-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE) to an aqueous solution of DNA has been studied in more detail. The extent of reaction and the relative yields of N2- and N7-products was measured over the range of pH 4--7. The depurination following reaction at the N7-position of guanine was found to have a half-life of 3 h. Reaction of the isomeric 7 alpha,8 beta-dihydroxy-9 alpha, 10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]-pyrene (syn-BPDE) with DNA gave the expected N2- and no N7-guanine product. When either benzo[a]pyrene or anti-BPDE was added to mouse embryo or Chinese hamster V79 cells respectively, a major N2-guanine product and a very minor adenine product were isolated from the DNA, but no N7-guanine product was detected.     

Synthesis and insecticidal activity of novel N-oxydihydropyrroles: 4-hydroxy-3-mesityl-1-methoxymethoxy derivatives with various substituents at the 5-position

This paper reports the synthesis and insecticidal activity of a series of novel 4-hydroxy-3-mesityl-1-methoxymethoxy-1,5-dihydro-2H-pyrrol-2-one derivatives, in which the substituents at the 5-position were varied with a number of alkyl and spirocycloalkyl groups. Investigation of the structure-activity relationships revealed that small alkyl and spirocyclohexyl groups had a favorable effect on the insecticidal activity of these agents against Myzus persicae.     

Biological variation responses in fMLP-OMe analogs, introducing bulky protecting groups on the side-chain of hydrophilic residues at position 2.

for-Met-Ser(Bzl)-Phe-OMe, for-Met-Cys(Bzl)-Phe-OMe, for-Met-Tyr(Bzl)-Phe-OMe and for-Met-Lys(Z)-Phe-OMe were synthesized to investigate the importance of a bulky protecting group on the side-chain of a hydrophilic residue at position 2 on the biological activities of human neutrophils. Our results indicate that these compounds do not trigger a good chemotactic response, which, in any case, is not improved with respect to that induced by the analogs with the unprotected residues. Instead, both superoxide anion production and, particularly, lysozyme release are more efficient.     

Antiplasmodial and antitumor activity of dihydroartemisinin analogs derived via the aza-Michael addition reaction

A series of dihydroartemisinin derivatives were synthesized via an aza-Michael addition reaction to a dihydroartemisinin-based acrylate and were evaluated for antiplasmodial and antitumor activity. The target compounds showed excellent antiplasmodial activity, with dihydroartemisinin derivatives 5, 7, 9 and 13 exhibiting IC₅₀ values of ?10 nM against both D10 and Dd2 strains of Plasmodium falciparum. Derivative 4d was the most active against the HeLa cancer cell line, with an IC₅₀ of 0.37 μM and the highest tumor specificity.     

Ethidium binding to deoxyribonucleic acid: spectrophotometric analysis of analogs with amino, azido, and hydrogen substituents

The DNA–ligand interactions of a series of phenanthridinium compounds with various combinations of amino, azido, and hydrogen functions at R₃ and R₈ were examined to determine the contribution of these particular substituents to ligand binding. Spectrophometric titrations using calf-thymus DNA emphasized the importance of amino substituents in conferring a strong interaction and also stabilizing the interaction against reversal by high ionic strength. Although azido groups were not as effective as amino groups, they were more effective than hydrogen functions in enhancing the interaction. Furthermore, an amino substitution at R₈ was consistently, though only slightly, more effective than an amino substituent at R₃. The results from superhelical titrations using plasmid pBR322 DNA demonstrated that analogs with amino and/or azido functions at both R₃ and R₈ produced the greatest unwinding, and compounds with an amino or an azido function at R₈ proved more effective than those with the corresponding amino or azido substituent at R₃.     

Effect of various substituents in the 6-position on the relative carcinogenic activity of a series of benzo[a]pyrene derivatives

To test the hypothesis that polycyclic aromatic hydrocarbons capable of being converted to a reactive ester of the mesohydroxymethyl metabolite would be carcinogenic, a series of 6-substituted derivatives of benzo[a]pyrene (B[a]P) were tested for carcinogenicity in Sprague-Dawley rats by subcutaneous injection of the compound in sesame oil on alternate days for 30 doses. At the 0.2-μmol dose level B[a]P, 6-acetoxymethyl(6-AcOCH₂)B[a]P, 6-hydroxymethyl(6-HOCH₂)B[a]P, 6-methyl(6-CH₃)B[a]P and 6-benzoyloxymethyl(6-BzOCH₂)B[a]P were nearly equipotent, 6-formyl(6-OCH)-and 6-chloromethyl(6-ClCH₂)B[a]P were less active, and 6-methoxymethyl (6-MeOCH₂)B[a]P was inactive. At lower doses the order of potency was estimated to be: 6-AcOCH₂- = 6-HOCH₂- = or > B[a]P > 6-CH₂- > 6-BzOCH₂- > 6-ClCH₂- > 6-OCH- > 6-BrCH₂B[a]P. Incubation of these compounds in the presence of cofactors or cofactors plus a microsomal preparation of rat subcutis indicated that enzymic activation was necessary for metabolism to highly polar products and for conversion of 6-AcOCH₂-, 6-BzOCH₂- and 6-OCHB[a]P to 6-HOCH₂B[a]P. The halomethyl compounds were converted to 6-HOCH₂B[a]P in the absence of enzyme by hydrolysis. 6-MeOCH₂B[a]P was unchanged in this system. These observations are consistent with the foregoing hypothesis with regard to derivatives of B[a]P and demonstrate that compounds of this series that are capable of conversion to the 6-HOCH₂-derivatives are carcinogenic.     

The synthesis of 5-substituted ring E analogs of methyllycaconitine via the Suzuki-Miyaura cross-coupling reaction

Novel 3,5-disubstituted ring E analogs of methyllycaconitine were prepared and evaluated in nicotinic acetylcholine receptor binding assays. The desired analogs were prepared through the Suzuki-Miyaura cross-coupling reaction of methyl 5-bromo-nicotinate. The Suzuki-Miyaura cross-coupling reactions of pyridines with electron withdrawing substituents have not been extensively described previously.     

PDZ7 of glutamate receptor interacting protein binds to its target via a novel hydrophobic surface area

Glutamate receptor interacting protein 1 (GRIP1) is a scaffold protein composed of seven PDZ (Postsynaptic synaptic density-95/Discs large/Zona occludens-1) domains. The protein plays important roles in the synaptic targeting of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. The interaction between GRIP1 PDZ7 and a Ras guanine nucleotide exchange factor, GRASP-1, regulates synaptic distribution of AMPA receptors. Here, we describe the three-dimensional structure of GRIP1 PDZ7 determined by NMR spectroscopy. GRIP1 PDZ7 contains a closed carboxyl group-binding pocket and a narrow alphaB/betaB-groove that is not likely to bind to classical PDZ ligands. Unexpectedly, GRIP1 PDZ7 contains a large solvent-exposed hydrophobic surface at a site distinct from the conventional ligand-binding alphaB/betaB-groove. NMR titration experiments show that GRIP1 PDZ7 binds to GRASP-1 via this hydrophobic surface. Our data uncover a novel PDZ domain-mediated protein interaction mode that may be responsible for multimerization of other PDZ domain-containing scaffold proteins.     

Methylation of 1-, 3-, 7-, 9-, and N6-methyladenines bearing a methoxyl group at the N6-position: a synthesis of 7,9-dimethyladenine

The effect of the N6-methoxy group on regioselectivity in methylation of all five possible isomers of N-methyladenine has been investigated. The methoxyl group attached to all these isomers orients methylation to a considerable extent to nitrogen(s) in the same pyrimidine or imidazole moiety that the original N-methyl group is attached to. On the basis of the results of the present methylation study, 7,9-dimethyladeninium perchlorate has been synthesized from 7- or 9-methyl-N6-methoxyadenine.