Novel spirosuccinimide aldose reductase inhibitors derived from isoquinoline-1,3-diones: 2-[(4-bromo-2-fluorophenyl)methyl]-6- fluorospiro[isoquinoline-4(1H),3'-pyrrolidine]-1,2',3,5'(2H)-tetrone and congeners. 1

Regio- and Atroposelective Ring-Opening of 1H-Benzo[4,5]oxazolopyridinones

The development of new methods for regio- and stereoselective activation of C-O bonds in ethers holds significant promise for synthetic chemistry, offering advantages in terms of environmental sustainability and economic efficiency. Moreover, the C-N atropisomers represent a fascinating and crucial chiral system, extensively found in natural products, pharmaceutical leads, and the frameworks of advanced materials. In this work, we have introduced a nickel-catalyzed regio- and enantioselective carbon-oxygen arylation reaction for atroposelective synthesis of N-arylisoquinoline-1,3(2H,4H)-diones. The high regioselectivity of C-O cleavage benefits from the high stability of the in situ formed (amido)ethenolate via oxidative addition. Additionally, the self-activation of the aryl C-O bond facilitates the reaction under mild conditions, leading to outstanding enantioselectivities. The diverse post-functionalizations of the axially chiral isoquinoline-1,3(2H,4H)-diones further highlighted the utility of this protocol in preparing valuable C-N atropisomers, including the chiral phosphine ligands.

Visible-Light-Driven Bifunctional Photocatalytic Radical-Cascade Selenocyanation/Cyclization of Acrylamides with KSeCN

A visible-light-induced radical-cascade selenocyanation/cyclization of N-alkyl-N-methacryloyl benzamides, 2-aryl-N-acryloyl indoles, and N-methacryloyl-2-phenylbenzimidazoles with potassium isoselenocyanate (KSeCN) was developed. The reactions were carried out with inexpensive KSeCN as a selenocyanation reagent, potassium persulfate as an oxidant, 2,4,6-triphenylpyrylium tetrafluoroborate as a bifunctional catalyst for phase-transfer catalysis, and photocatalysis. A library of selenocyanate-containing isoquinoline-1,3(2H,4H)-diones, indolo[2,1-a]isoquinoline-6(5H)-ones, and benzimidazo[2,1-a]isoquinolin-6(5H)-ones were achieved in moderate to excellent yields at room temperature under visible-light and ambient conditions. Importantly, the present protocol features mild reaction conditions, large-scale synthesis, simple manipulation, product derivatization, good functional group, and heterocycle tolerance.

Biobased Spiroimides from Itaconic Acid and Formamides: Molecular Targets for a Novel Synthetic Application of Renewable Chemicals

Spiroimides exhibit a wide range of biological activities, such as anticonvulsant, antiarrhythmic, and antihyperglycemic activities. Herein, a novel synthetic application of renewable chemicals, itaconic acid and formamides, is described. Proper exploitation of the reactivity of itaconic acid and formamide allows for the development of an efficient synthetic approach for the production of several new biobased spiroimides, spiro[dihydroquinolin-2-one-succinimides] and spiro[indolin-2-one-glutarimides], in excellent overall yields (up to 98%).

Palladium catalyzed asymmetric allylic alkylation of isoquinolinedione derivatives in the preparation of quaternary carbon stereocenters

A highly enantioselective allylic alkylation of isoquinolinedione derivatives under palladium catalysis was developed in the preparation of quaternary carbon stereocenters. Under standard reaction conditions, excellent yields and enantioselectivities were realized and the products could be transformed into dihydroisoquinolone with vicinal chiral carbon centers or THIQ core structures in short steps with high yields.

Visible-light-promoted acyl radical cascade reaction for accessing acylated isoquinoline-1,3(2H,4H)-dione derivatives

A visible-light-promoted radical acylation/cyclization cascade reaction of N-methacryloylbenzamides with α-keto acids was developed to construct acylated isoquinoline-dione derivatives.

Enantioselective synthesis of quaternary 3,4-dihydroisoquinolinones via Heck carbonylation reactions: development and application to the synthesis of Minalrestat analogues

Minalrestat and its analogues represent structurally novel aldose reductase inhibitors, and the asymmetric synthesis of such pharmaceutically privileged molecules has not been reported yet. We have developed a palladium-catalyzed enantioselective intramolecular carbonylative Heck reaction by using formate esters as the source of CO, which represents the first enantioselective synthesis of quaternary 3,4-dihydroisoquinolines. The reaction provides a facile and efficient method for the synthesis of enantiopure nitrogen-containing heterocyclic compounds bearing an all-carbon quaternary stereocenter. The reaction has been successfully applied to the first asymmetric synthesis of Minalrestat analogues.

Enantioselective synthesis of isoquinoline-1,3(2H,4H)-dione derivatives via a chiral phosphoric acid catalyzed aza-Friedel-Crafts reaction

A highly enantioselective aza-Friedel-Crafts reaction of structurally new ketimines with indoles and pyrrole is developed by using a chiral phosphoric acid as the catalyst. This protocol enables the first enantioselective synthesis of isoquinoline-1,3(2H,4H)-dione derivatives in good to excellent yields (up to 99% yield) and excellent enantioselectivities (up to >99% ee).

Assembly of Diverse Spirocyclic Pyrrolidines via Transient Directing Group Enabled Ortho-C(sp2)-H Alkylation of Benzaldehydes

A diversity-oriented synthesis of useful spirocyclic pyrrolidines was successfully accomplished via late-stage cascade reactions of o-succinimide-substituted benzaldehydes. A catalytic amount of aniline as a transient directing group was efficient for the ruthenium-catalyzed ortho-C(sp²)-H alkylation of benzaldehyde with maleimide. The in situ formed imine overrided a series of other traditional directing groups with excellent site selectivities. More importantly, only 0.5 mol % of ruthenium catalyst was sufficient for a 100 mmol scale-up reaction without column chromatography purification.

Investigation of a novel series of 2-hydroxyisoquinoline-1,3(2H,4H)-diones as human immunodeficiency virus type 1 integrase inhibitors

We report herein further insight into the biological activities displayed by a series of 2-hydroxyisoquinoline-1,3(2H,4H)-diones (HIDs). Substitution of the N-hydroxyimide two-metal binding pharmacophore at position 4 by carboxamido side chains was previously shown by us to be fruitful for this scaffold, since strong human immunodeficiency virus type 1 integrase (HIV-1 IN) inhibitors in the low nanomolar range associated with low micromolar anti-HIV activities were obtained. We investigated the influence of substitution at position 7 on biological activity. Introduction of electron-withdrawing functional groups such as the nitro moiety at position 7 led to a noticeable improvement of antiviral activity, down to low nanomolar anti-HIV potencies, with advantageous therapeutic indexes going close to those of the clinically used raltegravir and retained potencies against a panel of IN mutants.

Synthesis of isoquinoline-1,3(2H,4H)-dione derivatives via cascade reactions of N-alkyl-N-methacryloyl benzamide with aryl aldehydes

A cascade reaction between N-alkyl-N-methacryloylbenzamide and aryl aldehydes was developed to generate isoquinoline-1,3(2H,4H)-dione derivatives.

Photo-induced cycloaddition reactions of α-diketones and transformations of the photocycloadducts

Photocycloaddition, along with subsequent transformation of the photocycloadducts, provides expeditious ways to construct various structures. The photo-induced reactions of α-diketones have been reported to proceed via different reaction pathways with the involvement of one or two of the carbonyl groups. Photoinduced reactions of cyclic α-diketones including N-acetylisatin, phenanthrenequinone and isoquinolinetrione with different C=C containing compounds could take place via [2 + 2], [4 + 2] or [4 + 4] photocycloaddition pathways. We have investigated the photoreactions of these cyclic α-diketones with different types of alkenes and alkynes, with a focus on the unusual cascade reactions initiated by the photocycloaddition reactions of these cyclic α-diketones and the applications of these photocycloaddition reactions along with the transformation of the photocycloadducts. In this paper, we discuss the diverse photo-cycloaddition pathways found in the photocycloaddition of o-diones leading to various photocycloadducts and the potential applications of these reactions via further transformation reactions of the adducts.

Methyl 4'-isobutyl-2,2'-dimethyl-1,3-dioxo-2,3-dihydro-1H,4'H-spiro-[iso-quinoline-4,5'-oxazole]-4'-carboxyl-ate

In the isoquinoline ring system of the title mol-ecule, C(19)H(22)N(2)O(5), the N-heterocyclic ring is in a half-boat conformation. The dioxa-2-aza-spiro ring is essentially planar [maximum deviation = 0.042 (1) Å] and forms a dihedral angle of 81.85 (4)° with the benzene ring. In the crystal, the mol-ecules are linked via inter-molecular C-H⋯O hydrogen bonds into chains along [010].

(1S*,4'S*,5R*)-1-Isobutyl-5-meth-oxy-2',3-dimethyl-4,6-dioxa-2-aza-spiro-[bicyclo-[3.2.0]hept-2-ene-7,4'-isoquinoline]-1',3'(2'H,4'H)-dione

In the isoquinoline ring system of the title compound, C₁₉H₂₂N₂O₅, the N-heterocyclic ring is in a half-chair conformation. The dioxa-2-aza­spiro ring is essentially planar [maximum deviation of 0.025 (1) Å] and forms a dihedral angle of 23.51 (5)° with the benzene ring. In the crystal, mol­ecules are linked via weak inter­molecular C—H⋯O and C—H⋯N hydrogen bonds into chains along [010].

(1S*,4'S*,5R*)-1-Isopropyl-5-meth-oxy-2',3-dimethyl-4,6-dioxa-2-aza-spiro-[bicyclo-[3.2.0]hept-2-ene-7,4'-isoquinoline]-1',3'(2'H,4'H)-dione

In the isoquinoline ring system of the title mol­ecule, C₁₈H₂₀N₂O₅, the N-heterocyclic ring is in a half-boat conformation. The dioxa-2-aza­spiro ring is essentially planar, with a maximum deviation of 0.029 (1) Å, and makes a dihedral angle of 30.63 (5)° with the benzene ring. The mol­ecular structure is stabilized by a weak intra­molecular C—H⋯O hydrogen bond, which generates a S(6) ring motif. In the crystal, mol­ecules are linked via weak inter­molecular C—H⋯O hydrogen bonds into a three-dimensional supra­molecular network. Additional stabilization is provided by π–π stacking inter­actions between symmetry-related benzene rings with a centroid–centroid distance of 3.6507 (5) Å.

Design and synthesis of potent and selective aldose reductase inhibitors based on pyridylthiadiazine scaffold

A series of pyrido[2,3-e]-[1,2,4]-thiadiazine 1,1-dioxide acetic acid derivatives were synthesized and tested for their inhibitory activity against aldose reductase (ALR2). These derivatives were found to be potent aldose reductase inhibitors with IC50 values ranging from 0.038 μM to 11.29 μM. Most but not all of them showed a strong ALR2 inhibition activity and significant selectivity, which were further supported by docking studies. Of these inhibitors, compound 7d exhibited highest inhibition activity. Structure-activity relationship studies indicate the requirement of N2-benzyl group with electron-withdrawing substituents and N4-acetic acid group in the pyridothiadiazine scaffold.

4-[(2,4-Dimethyl-thia-zol-5-yl)meth-yl]-4-hydr-oxy-2-methyl-isoquinoline-1,3(2H,4H)-dione

In the title isoquinoline-dione derivative, C(16)H(16)N(2)O(3)S, the piperidine ring in the tetra-hydro-isoquinoline ring system adopts a distorted envelope conformation. The thia-zole ring is essentially planar [maximum deviation = 0.004 (1) Å] and is inclined at a dihedral angle of 31.08 (3)° with respect to the mean plane through the tetra-hydro-isoquinoline ring system. In the crystal structure, inter-molecular O-H⋯O and C-H⋯O inter-actions link adjacent mol-ecules into a three-dimensional extended network. The crystal structure is further stabilized by weak C-H⋯π inter-actions.

2'-Methyl-3,5-diphenyl-spiro-[4,6-dioxa-2-aza-bicyclo-[3.2.0]hept-2-ene-7,4'-iso-quinoline]-1',3'(2'H,4'H)-dione

In the title compound, C(25)H(18)N(2)O(4), the tetra-hydro-pyridine ring adopts a distorted envelope conformation with the spiro C atom at the flap position [deviation = 0.470 (2) Å]. The dihydro-oxazole ring is planar (r.m.s. deviation = 0.013 Å) and it makes dihedral angles of 73.43 (8) and 4.24 (8)° with the two attached phenyl rings. The dihedral angle between oxetane and oxazole planes is 67.44 (9)°. In the crystal structure, C-H⋯O hydrogen bonds link neighbouring mol-ecules into zigzag chains along the b axis and these chains are linked via C-H⋯π inter-actions.

4-[(2,4-Dimethyl-1,3-oxazol-5-yl)meth-yl]-4-hydr-oxy-2-methyl-isoquinoline-1,3(2H,4H)-dione

In the title isoquinolinedione derivative, C₁₆H₁₆N₂O₄, the piperidine ring in the tetra­hydro­isoquinoline unit adopts a half-boat conformation. The essentially planar oxazole ring [maximum deviation = 0.004 (2) Å] is inclined at a dihedral angle of 36.00 (8)° to the tetra­hydro­isoquinoline unit. In the crystal structure, pairs of inter­molecular C—H⋯O and O—H⋯N inter­actions link the mol­ecules into chains incorporating R₂²(9) ring motifs. Two neighbouring chains are further inter­connected by inter­molecular C—H⋯O inter­actions into chains two mol­ecules wide along the a axis.

Stability and Hydrolysis Kinetics of Spirosuccinimide type Inhibitors of Aldose Reductase in Aqueous Solution and Retardation of Their Hydrolysis by the Target enzyme

The stability and the hydrolysis kinetics of spirosuccinimide type aldose reductase (AR) inhibitors, SX-3030 (racemate) and its optical enantiomers (R- and S-isomers), were investigated in aqueous solution. The hydrolysis followed pseudo-first-order kinetics and showed significant pH dependence. Maximum solution stability was observed below pH 2.4, whereas the hydrolysis was gradually catalyzed by hydroxide ion at neutral to alkaline pH while the compounds exhibiting moderate pH-independent stability at acidic to neutral conditions (pH 4-7) to enable oral administration. A pK of 3.7 was obtained from the pH-rate profile, but this kinetically derived pK is approximately 2 pH units below the pK of the parent compounds, suggesting the presence of an acidic intermediate involved in the hydrolysis process. These findings, together with structural analysis, support the notion that the hydrolysis would proceed via nucleophilic attack of a water molecule or hydroxide ion on the scissile carbonyl bond of the succinimide ring to form a succinamic acid intermediate that has a beta-keto acid structure, followed by decarboxylation to give a racemized succinimide ring-opened product. On the other hand, the interconversion of the R- and S-isomers did not occur during hydrolysis; however, the hydrolysis of the R-isomer was markedly suppressed by the target enzyme AR whereas that of the S-isomer was not, indicating a high degree of complementarity of interacting surfaces between the R-isomer and the enzyme. The results in the present study could provide useful clues for facilitating the appropriate stabilization strategies as well as for evaluating the pharmacological effects on target tissues in vivo, and suggested that the R-isomer may be a suitable candidate as AR inhibitor.

Unusual binding mode of the 2S4R stereoisomer of the potent aldose reductase cyclic imide inhibitor fidarestat (2S4S) in the 15 K crystal structure of the ternary complex refined at 0.78 A resolution: implications for the inhibition mechanism

The structure of human aldose reductase in complex with the 2 S4 R stereoisomer of the potent inhibitor Fidarestat ((2 S,4 S)-6-fluoro-2',5'-dioxospiro-[chroman-4,4'-imidazoline]-2-carboxamide) was determined at 15 K and a resolution of 0.78 A. The structure of the complex provides experimental evidence for the inhibition mechanism in which Fidarestat is initially bound neutral and then becomes negatively charged by donating the proton at the 1'-position nitrogen of the cyclic imide ring to the N2 atom of the catalytic His110.

Stereospecific recognition of a spirosuccinimide type aldose reductase inhibitor (AS-3201) by plasma proteins: A significant role of specific binding by serum albumin in the improved potency and stability

AS-3201 [(3R)-2'-(4-bromo-2-fluorobenzyl)spiro[pyrrolidine-3,4'(1'H)-pyrrolo[1,2-a]pyrazine]-1',2,3',5(2'H)-tetrone] is a structurally novel and stereospecifically potent aldose reductase (AKR1B; EC 1.1.1.21) inhibitor, which contains a succinimide ring that undergoes ring-opening at physiological pH levels. To delineate intermolecular interactions governing its favorable pharmacokinetic profile, the interaction of AS-3201 (R-isomer) with plasma proteins, especially human serum albumin (HSA), was examined in comparison with that of the optical antipode (S-isomer). Fluorescence, kinetic, and high-performance frontal analyses showed that the R-isomer is more strongly bound than the S-isomer to sites I and II on HSA, and the R-isomer is particularly protected from hydrolysis, suggesting that the stable HSA-R-isomer complex contributes to its prolonged activity. The thermodynamic parameters for the specific binding indicated that in addition to hydrophobic interactions, hydrogen bonds contribute significantly to the R-isomer complex formation. (13)C NMR observations of the succinimide ring (5-(13)C enriched), which are sensitive to its ionization state, suggested the presence of a hydrogen bond between the R-isomer and HSA, and (19)F NMR of the pendent benzyl ring (2-(19)F) evaluated the equilibrium exchange dynamics between the specific sites. Furthermore, fatty acid binding or glycation (both are site II-oriented perturbations) inhibited the binding to one of the specific sites and reduced the stereospecificity of HSA toward the isomers, although the clinical influence of these perturbations on the R-isomer binding ratio seemed to be minor. Thus, the difference in the interaction mode at site II might be a major cause of the stereospecificity; this is discussed on the basis of putative binding modes. The present results, together with preliminary absorption and distribution profiles, provide valuable information on the stereospecific pharmacokinetic and pharmacodynamic properties of the R-isomer relevant for the therapeutic treatment of diabetic complications.

Design and synthesis of highly potent and selective (2-arylcarbamoyl-phenoxy)-acetic acid inhibitors of aldose reductase for treatment of chronic diabetic complications

Recent efforts to identify treatments for chronic diabetic complications have resulted in the discovery of a novel series of highly potent and selective (2-arylcarbamoyl-phenoxy)-acetic acid aldose reductase inhibitors. The compound class features a core template that utilizes an intramolecular hydrogen bond to position the key structural elements of the pharmacophore in a conformation, which promotes a high binding affinity. The lead candidate, example 40, 5-fluoro-2-(4-bromo-2-fluoro-benzylthiocarbamoyl)-phenoxyacetic acid, inhibits aldose reductase with an IC(50) of 30 nM, while being 1100 times less active against aldehyde reductase, a related enzyme involved in the detoxification of reactive aldehydes. In addition, example 40 lowers nerve sorbitol levels with an ED(50) of 31 mg/kg/d po in the 4-day STZ-induced diabetic rat model.

Synthesis and aldose reductase inhibitory activities of novel thienocinnolinone derivatives

A novel series of tetrahydrothieno[2,3-h]cinnolinone derivatives were synthesized and evaluated in vitro for their ability to inhibit aldose reductase (ALR2), an enzyme involved in the appearance of diabetic complications. Compounds 2e and 2j exert a remarkable inhibitory effect, with IC(50) of 7.6 and 18 microM, respectively. These compounds incorporate a valid pharmacophore for aldose reductase inhibitory activity represented by a thienocinnolinone template linked through a pentamethylene spacer to a carboxylic function.

Ultrahigh resolution drug design. II. Atomic resolution structures of human aldose reductase holoenzyme complexed with fidarestat and minalrestat: Implications for the binding of cyclic imide inhibitors

The X-ray structures of human aldose reductase holoenzyme in complex with the inhibitors Fidarestat (SNK-860) and Minalrestat (WAY-509) were determined at atomic resolutions of 0.92 A and 1.1 A, respectively. The hydantoin and succinimide moieties of the inhibitors interacted with the conserved anion-binding site located between the nicotinamide ring of the coenzyme and active site residues Tyr48, His110, and Trp111. Minalrestat's hydrophobic isoquinoline ring was bound in an adjacent pocket lined by residues Trp20, Phe122, and Trp219, with the bromo-fluorobenzyl group inside the "specificity" pocket. The interactions between Minalrestat's bromo-fluorobenzyl group and the enzyme include the stacking against the side-chain of Trp111 as well as hydrogen bonding distances with residues Leu300 and Thr113. The carbamoyl group in Fidarestat formed a hydrogen bond with the main-chain nitrogen atom of Leu300. The atomic resolution refinement allowed the positioning of hydrogen atoms and accurate determination of bond lengths of the inhibitors, coenzyme NADP+ and active-site residue His110. The 1'-position nitrogen atom in the hydantoin and succinimide moieties of Fidarestat and Minalrestat, respectively, form a hydrogen bond with the Nepsilon2 atom of His 110. For Fidarestat, the electron density indicated two possible positions for the H-atom in this bond. Furthermore, both native and anomalous difference maps indicated the replacement of a water molecule linked to His110 by a Cl-ion. These observations suggest a mechanism in which Fidarestat is bound protonated and becomes negatively charged by donating the proton to His110, which may have important implications on drug design.

Minalrestat and leukocyte migration in diabetes mellitus

BACKGROUND

We recently demonstrated that aldose reductase inhibition was effective in restoring the reduced migratory capacity of leukocytes in diabetic rats. To investigate the mechanism(s) involved in the restoring effect, we used minalrestat, an aldose reductase inhibitor.

METHODS

In sodium pentobarbital-anesthetized (40 mg/kg, intraperitoneally) alloxan-diabetic or galactosemic male Wistar rats, the internal spermatic fascia was exteriorized, and the number of leukocytes rolling along the venular endothelium and the number of leukocytes sticking to the vascular wall after topical application of zymosan-activated plasma or leukotriene B(4) (1 ng/ml), as well as after the application of a local irritant stimulus (carrageenan, 100 microg), were determined using intravital microscopy. Data from animals that were treated with and those that were not treated with minalrestat (10 mg/kg/d by gavage) were compared.

RESULTS

The reduced number of leukocytes rolling along the venular endothelium (by about 70%) and the number of adhered and migrated leukocytes in postcapillary venules (by 60%) were significantly restored to control values after minalrestat treatment. Total or differential leukocyte counts, venular blood flow velocity or wall shear rate were not altered by minalrestat treatment. The expression of ICAM-1 and P-selectin, cell adhesion molecules involved in the interaction of leukocyte-endothelium, reduced in diabetic rats was restored by minalrestat treatment.

CONCLUSION

We conclude that an enhanced flux through the polyol pathway might be involved in the reduced expression of ICAM-1 and P-selectin contributing to the impaired leukocyte-endothelial interactions in diabetes mellitus and that aldose reductase inhibition restores the defect, restoring the reduced expression.

Minalrestat, an aldose reductase inhibitor, corrects the impaired microvascular reactivity in diabetes

We demonstrated that aldose reductase inhibition corrects the impaired microvascular responses to inflammatory mediators in diabetic rats. To study the mechanism involved in the restoring effect of aldose reductase inhibition, we examined the effects of minalrestat, another aldose reductase inhibitor, on the responses of mesenteric microvessels studied in vivo to permeability-increasing agents in diabetic and galactosemic rats. The diabetic group was treated from 3 days after the alloxan injection with minalrestat (10 mg/kg/day) for 30 days and the minalrestat treatment (10 mg/kg/day/7 days) of galactosemic rats started concomitantly with the induction of galactosemia. The mesenteric microvessel reactivity was studied using intravital microscopy and changes in vessel diameters were estimated after the topical application of vasoactive agents. The impaired responses to bradykinin, histamine, and platelet-activating factor of arterioles and venules observed in diabetic and galactosemic rats were completely prevented by minalrestat. Neither diabetes nor galactosemia affected responses to acetylcholine and sodium nitroprusside. Responses to these agents were not modified by aldose reductase inhibition. The restoring effect of minalrestat was reversed by inhibition of nitric oxide (NO) synthesis with N(omega)-nitro-L-arginine methyl ester, by blocking K(+) channel with tetraethylammonium but not by cyclooxygenase inhibition with diclofenac. Therefore, we concluded that NO, membrane hyperpolarization, but not cyclooxygenase products are involved in the beneficial effect of minalrestat on the microvascular reactivity in diabetes. Together, these findings led us to suggest that aldose reductase inhibition might ameliorate diabetic complications through the correction of the altered microvascular reactivity by a mechanism that involves NO and membrane hyperpolarization.