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A series of new anti-inflammatory steroidal antedrugs with C-16,17-isoxazoline ring system were synthesized and their pharmacological activities were evaluated. We reported earlier that these compounds are promising antedrugs based on the results of 5-day rat croton oil ear edema assay. In the present study, most of these compounds showed high binding affinities to the glucocorticoid receptor of liver cytosol. 21-acetyloxy-9alpha-fluoro-11beta-hydroxy-3,20-dioxo-1,4-pregnadieno [16alpha,17alpha-d] isoxazoline (FP-ISO-21AC) and 11beta,21-dihydroxy-9alpha-fluoro-3,20-dioxo-1,4-pregnadieno [16alpha,17alpha-d] isoxazoline (FP-ISO-21OH) were found 5.0-, 5.3-fold more potent than prednisolone, respectively. Inhibitory effects of the antedrugs on the nitric oxide (NO) production were assessed using LPS-stimulated RAW 264.7 murine macrophage cells. All these steroidal antedrugs exhibited concentration-dependent inhibition of NO production, but their relative potencies were lower than prednisolone. In vitro metabolism study in rat plasma showed that FP-ISO-21AC and 21-acetyloxy-9alpha-fluoro-11beta-hydroxy-3,20-dioxo-1,4-pregnadieno [16alpha,17alpha-d]-3'-hydroxyiminoformyl isoxazoline (FP-OXIM-21AC) were hydrolyzed rapidly, with the half-lives of 2.1 and 4.2 min, respectively. The half-lives of FP-ISO-21OH and 11beta,21-dihydroxy-9alpha-fluoro-3,20-dioxo-1,4-pregnadieno [16alpha,17alpha-d]-3'-hydroxyiminoformyl isoxazoline (FP-OXIM-21OH) were 92.2 and 110.2 min, respectively.
4-Sulfenyl-2-carbamoyl-4-isoxazolin-3-ones (4) were designed on the basis of biological isosterism and prepared in four steps. Some of these compounds showed sufficient pre-emergent herbicidal activities against various kinds of weeds. Among the synthesized compounds, 2-(N-(4-chlorophenyl)-N-isopropylcarbamoyl)-4-ethylthio-5-methyl-4 -isoxazolin-3-one (4cd) exhibited the most promising activity.
The synthesis of novel imidazolyl substituted delta2-isoxazoline libraries are currently of high interest. We report here in the full details of a study leading to the synthesis and antifungal activities of 3-(-2-butyl-4-chloro-1H-imidazolyl)-substituted delta2-isoxazolines. The solution phase synthesis of the title compounds was accomplished via 1,3-dipolar cycloaddition of in situ generated nitryl oxides from aldoximes with mono substituted alkenes to obtain the compound libraries contain an imidazole functionality in addition to the isoxazoline rings. The newly synthesized compounds when tested in vitro in solid agar culture exerted a potent antifungal activity against Aspergillus flavus, Fusarium moniliforme and Botrydiplodia theobromae also MIC values were determined. The title 5-substituted-3-imidazolyl-delta2-isoxazoline compounds represent a novel class of potent antifungal agents.
4,5-Diphenyl-4-isoxazolines (13a-k) possessing a variety of substituents (H, F, MeS, MeSO2) at the para position of one of the phenyl rings were synthesized for evaluation as analgesic and selective cyclooxygenase-2 (COX-2) inhibitory antiinflammatory (AI) agents. Although the 4,5-phenyl-4-isoxazolines (13a-d,f), which do not have a C-3 Me substituent, exhibited potent analgesic and AI activities, those compounds evaluated (13a, 13b, 13h, and 13k) were not selective inhibitors of COX-2. In contrast, 2,3-dimethyl-5-(4-methylsulfonylphenyl)-4-phenyl-4-isoxazoline (13j) exhibited excellent analgesic and AI activities, and it was a potent and selective COX-2 inhibitor (COX-1, IC(50) = 258 microM; COX-2, IC(50) = 0.004 microM). A related compound 13k having a F substituent at the para position of the 4-phenyl ring was also a selective (SI = 3162) but less potent (IC(50) = 0.0316 microM) inhibitor of COX-2 than 13j. A molecular modeling (docking study) for 13j showed that the S atom of the MeSO2 substituent is positioned about 6.46 A inside the entrance to the COX-2 secondary pocket (Val(523)) and that a C-3 Me (13j, 13k) central isoxazoline ring substituent is crucial to selective inhibition of COX-2 for this class of compounds.
Some 3-glycosyl-5-aryl-2-isoxazolines were studied in the gas phase under electron ionization (EI) conditions in order to elucidate their behavior. These derivatives showed an interesting rearrangement involving opening of the heterocyclic ring with a concomitant ring closing to afford a new isoxazoline derivative. The first step of this reaction was the less common cleavage of the heterocyclic C(5)-O bond. The 5-aryl substituent was responsible for the pseudobenzylic stabilization of the new isoxazoline derivative. EI tandem mass spectrometry and EI high-resolution mass spectrometry allowed the elucidation of fragmentation pathways. Copyright 1999 John Wiley & Sons, Ltd.
A series of 2-alkoxyimino-N-(2-isoxazolin-3-ylmethyl)acetamides and related compounds were synthesized and their antiviral activities against human influenza A virus were assessed. Studies of the structure-activity relationships revealed the strongest antiviral activity when position-5 of the isoxazoline ring was substituted with a tert-butyl group. When the alkoxyimino moiety was substituted with a methyl, ethyl, isopropyl or allyl group, good antiviral activity was obtained. Among the geometrical isomers at the oxime moiety, the E-isomers were more active than the Z-isomers. Among the compounds examined, (E)-2-allyloxyimino-2-cyano-N-(5-tert-butyl-2-isoxazolin-3-ylmethyl)acetamide (1j) was the most active inhibitor with an EC(50) of 3 microg/mL in vitro.
A series of delta 2-isoxazoline derivatives structurally related to Broxaterol 1 and Falintolol 3 has been prepared and evaluated for their binding affinity to beta 1- and beta 2-adrenergic receptors. Among the tested compounds only the 3-isopropenyl anti derivative 4d is as active as the reference compounds. An electron-releasing group, probably operating through a pi-pi interaction, in the 3-position of the isoxazoline nucleus greatly enhances the affinity of the compounds. Conversely, the closest analogs of Broxaterol (3-bromo delta 2-isoxazolines 4a and 5a) are at least one order of magnitude less active than the model compound 1. Throughout the series of derivatives the anti stereoisomers are invariably more active than their syn counterparts.
Treatment of 2-acetoxy glycopyranosyl azides with Ph3P gave isoxazolines by ring closure of the phosphorimine. Coupling of in situ generated isoxazolines with acylating reagents gave mixtures of alpha- or beta-glycopyranosyl amides. The alpha/beta ratio depended upon the acylating reagent and metal salts employed. For example, coupling of isoxazoline 3 with Z-Asp-(SPy)-OBn in the presence of CuCl2 gave exclusively alpha-N-glucopyranosylasparagine derivative 8. This general procedure has been applied to mono-, di-, and trisaccharide systems.
UDP-3-O-[R-3-hydroxymyristoyl]-GlcNAc deacetylase (LpxC) is a zinc amidase that catalyzes the second step of lipid A biosynthesis in Gram negative bacteria. Known inhibitors of this enzyme are oxazolines incorporating a hydroxamic acid at the 4-position, which is believed to coordinate to the single essential zinc ion. A new structural class of inhibitors was designed to incorporate a more stable and more synthetically versatile isoxazoline core. The synthetic versatility of the isoxazoline allowed for a broad study of metal binding groups. Nine of 17 isoxazolines, each incorporating a different potential metal binding functional group, were found to exhibit enzyme inhibitory activity, including one that is more active than the corresponding hydroxamic acid. Additionally, a designed affinity label inhibits LpxC in a time-dependent manner.
Using isoxazoline XR299 (1a) as a starting point for the design of highly potent, long-duration GPIIb/IIIa antagonists, the effect of placing lipophilic substituents at positions alpha and beta to the carboxylate moiety was evaluated. Of the compounds studied, it was found that the n-butyl carbamate 24u exhibited superior potency and duration of ex vivo antiplatelet effects in dogs. Replacement of the benzamidin-4-yl moiety with alternative basic groups, elimination of the isoxazoline stereocenter, and reversal of the orientation of the isoxazoline ring resulted in lowered potency and/or duration of action.
4-Alkoxycarbonyl and aminocarbonyl-substituted isoxazoles undergo conjugate reduction to give delta2-isoxazolines on treatment with sodium borohydride and sodium trifluoroacetoxyborohydride, respectively. They are also alkylated at C5 through sonication with secondary and tertiary alkyl iodides in the presence of zinc dust and copper(I) iodide. These reactions are analogous to those observed with acrylates and acrylamides. The behavior is characteristic of the 4-substituted isoxazoles but not the 5-substituted regioisomers. The reductions of 4,5-disubstituted isoxazoles and the C5 alkylations of 4-substituted isoxazoles generally afford trans-4,5-disubstituted isoxazolines. Incorporating chiral auxiliaries into the alkoxycarbonyl group maintains this relative stereoselectivity. It does not provide significant levels of asymmetric induction in the reductions, but the alkylations occur with good levels of stereocontrol at both C4 and C5. Because both enantiomers of the auxiliaries are available, this provides access to either enantiomer of the products, in 93 to > or = 98% de. The methodology, therefore, provides a complementary approach to nitrile oxide cycloadditions to alkenes for the asymmetric synthesis of delta2-isoxazolines.
In aqueous solution, N-substituted isoxazolin-5-one derivatives, which occur in high amounts in seedlings of the tribe Vicieae, can be shown to undergo a proton exchange at C-4, indicative of their aromatic character. Under UV-light these different isoxazolin-5-one derivatives are then broken down, each following the same degradation scheme, some of them forming the well-known toxins of the genus Lathyrus. The loss of aromatic character and the addition of two water molecules is proposed as the underlying mechanism for this photolysis. The biochemical relation between isoxazolin-5-ones and the Lathyrus toxins is discussed.
The 3,5-isoxazolidinediones and 2-isoxazolin-5-ones demonstrated potent cytotoxicity against the growth of human Tmolt3 T cell leukemia, murine P388 and L1210 leukemias, as well as human HeLa-S3 uterine carcinoma and glioma tumor cell growth. The specificity of the 3,5-isoxazolidinedione and 2-isoxazoline-5-one derivatives as cytotoxic agents varied with the histological type of tumor cell. Selected compounds were active against solid HeLa uterine. KB nasopharynx, skin A431, SW-480 adenocarcinoma, osteosarcoma and glioma growth. Selected compounds demonstrated in vivo antineoplastic activity against Ehrlich ascites carcinoma growth. In L-1210 leukemia cells, the agents blocked DNA and protein synthesis at 25, 50 and 100 microM over 60 min. The agents were effective in reducing rate limiting enzymes in the de novo purine and pyrimidine pathways. In addition they suppressed dihydrofolate reductase and ribonucleoside reductase activities with moderate inhibition of DNA and RNA polymerase activities. DNA itself was not a target of the agents.
3-[2-(5-Nitro-2-furyl)vinylen]-2-isoxazoline (VIII) and 3-nitro-, 3-amino- and 3-acylaminostyryl-2-isoxazolines have been synthesized and tested for antibacterial activity. Compound (VIII) showed potent antibacterial activity in vitro against several strains of S. aureus and E. coli (two to eight times more active than furazolidone). None of the styryl derivatives exhibited significant activity.
The new enantiomerically pure 3-substituted-Delta(2)-isoxazolin-5-yl-ethanolamines (+)-6a/(-)-6b, (-)-6a/(+)-6b, and (+)-7a/(-)-7b, prepared via a 1,3-dipolar cycloaddition-based approach, were tested for their affinity at human beta(1)-, beta(2)-, and beta(3)-adrenergic receptor (beta-AR) subtypes stably expressed in CHO cells. The corresponding 3-isopropenyl derivatives (+)-5a/(-)-5b, (-)-5a/(+)-5b, and some isoxazole analogs were also tested. The binding affinities at the beta-ARs of the isoxazolinyl amino alcohols were significantly lower than those of the corresponding isoxazole derivatives. A stereochemical effect was observed, since the process of molecular recognition is predominantly controlled by the (S)-configuration of the stereogenic center located at the 5 position of the heterocycle rather than by that of the stereocenter carrying the secondary alcohol group. On the contrary, the stereochemical features marginally affected the efficacy response; as a matter of fact, functional tests carried out on Delta(2)-isoxazoline derivatives provided with a detectable binding affinity showed the overall profile of neutral antagonists at all three beta-AR subtypes.
The synthesized imidazolyl substituted delta2-isoxazolines were subjected to Phospholipase A(2) (PLA(2)) enzyme inhibitory activity against snake venom source and their structure-activity relationship with respect to different groups attached to this moiety is reported for the first time. The crystal structure of the compound 2-butyl-5-chloro-3H-imidazolyl-4-carbaldehyde oxime 2, an intermediate for the construction of isoxazolines is reported. These compounds exerted a significant PLA(2) enzyme inhibitory activity against group II PLA(2). The in vivo activity on mice of selected compounds 3bI and 3bIV shows the comparable anti-inflammatory activity with the known standard ursolic acid.
The salts, 2-methyl-5,5-disubstituted 4,5-dihydroisoxazolium methylsulfates comprising various substituents at the C-3 carbon atom were subjected to transformations. The structure of applied compounds permitted to monitor the effect of this factor on the transformation course of the 2-isoxazoline ring. The nucleophilic addition of cyanide anion to the selected salts enabled the obtaining of a next heterocyclic system of changed physicochemical and biological properties in comparison to the starting 2-isoxazolines. The diastereoselective hydrolysis of the cyanide group in 2-isoxazolidines by the bacteria strain Rhodococcus rhodochrous PCM 909 leads to the obtaining of a racemic mixture of the trans-hydroxyacid. The introduction of new functional groups into the heterocyclic ring made these compounds attractive objects for further chemical and microbial transformations and to study their biological activity.