abeo‐Taxane Diterpenoids from the Taiwanese Yew Taxus sumatrana

Chemical investigation of the acetonic extract of the leaves and twigs of Taxus sumatrana (Taxaceae) led to the isolation of four new taxane diterpene esters, taiwantaxins A–D ( 1 – 4 , resp.). Their structures were determined primarily on the basis of 1D‐ and 2D‐NMR techniques as well as MS. Compound 1 is a rearranged taxane diterpenoid possessing an opened oxetane ring moiety containing C(4), C(5), and C(20). The metabolites 2 and 3 belong to a 5/6/6 taxene system having a rare five‐membered γ‐lactone ring comprising C(8), C(9), C(10), and C(19). Compound 4 is an example of a taxane diterpene containing a 6/8/6 ring system with a tetrahydrofuran ring comprising C(2), C(3), C(4), and C(20). The 11(15→1)abeo‐taxane diterpenoids, taiwantaxins A–C ( 1 – 3 , resp.) are lacking an O‐bearing functionality at either C(13) or C(14). Compound 2 showed significant cytotoxic activity against human PC‐3 tumor cells.     

Three New Diketopiperazines from the Previously Uncultivable Marine Bacterium Gallaecimonas mangrovi HK‐28 Cultivated by iChip

The in situ application of iChip cultivation in mangrove sediment from Hainan province, China, led to the isolation of a novel bacterial species Gallaecimonas mangrovi HK‐28. The extract of G. mangrovi HK‐28 exhibited antibiotic activity against the aquatic pathogen Vibrio harveyi, and its chemical constituents were further investigated by bioactivity‐guided isolation. Three new diketopiperazines, gallaecimonamides A–C, were accordingly isolated from the AcOEt extract of the fermentation broth of G. mangrovi HK‐28. The planar structures of gallaecimonamides A–C were determined using HR‐ESI‐MS together with 1D‐ and 2D‐NMR. The absolute configurations of gallaecimonamides A–C were assigned by optical rotation, NOESY experiment and TDDFT ECD calculations. The in vitro antibacterial and antimalarial activities of gallaecimonamides A–C were assessed. Gallaecimonamide A was found to display antibacterial activity against V. harveyi with a MIC value of 50 μm . However, gallaecimonamides B and C showed no antibacterial activity against V. harveyi (MIC >300 μm ). In addition, all the isolates did not exhibit any inhibitory activities against V. parahaemolyticus (MIC>300 μm ) and Plasmodium falciparum W2 (EC₅₀>100 μg/mL).     

Characterization of the functional activity of botulinum neurotoxin subtype B6

Clostridium botulinum produces the highly potent neurotoxin, botulinum neurotoxin (BoNT), which is classified into seven serotypes (A–G); the subtype classification is confirmed by the diversity of amino acid sequences among the serotypes. BoNT from the Osaka05 strain is associated with type B infant botulism and has been classified as BoNT/B subtype B6 (BoNT/B6) by phylogenetic analysis and the antigenicity of its C‐terminal heavy chain (H_C) domain. However, the molecular bases for its properties, including its potency, are poorly understood. In this study, BoNT/B6 holotoxin was purified and the biological activity and receptor binding activity of BoNT/B6 compared with those of the previously‐characterized BoNT/B1 and BoNT/B2 subtypes. The derivative BoNT/B6 was found to be already nicked and in an activated form, indicating that endogenous protease production may be higher in this strain than in the other two strains. BoNT/B1 exhibited the greatest lethal activity in mice, followed by BoNT/B6, which is consistent with the sensitivity of PC12 cells. No significant differences were seen in the enzymatic activities of the BoNT/Bs against their substrate. H_C/B1 and H_C/B6 exhibited similar binding affinities to synaptotagmin II (SytII), which is a specific protein receptor for BoNT/B. Binding to the SytII/ganglioside complex is functionally related to the toxic action; however, the receptor recognition sites are conserved. These results suggest that the distinct characteristics and differences in biological sensitivity of BoNT/B6 may be attributable to the function of its H_c.domain.

     

Synthesis and Antioxidant Activity of New Norcantharidin Analogs

New norcantharidin analogs were designed and obtained as compounds with biological activity. As a starting material, exo‐7‐oxabicyclo[2.2.1]heptane‐2,3‐dicarboxylic acid anhydride was used. Three groups of compounds: dicarboximides, triazoles and thiazolidines were obtained in multistep reactions. The ¹H‐ and ¹³C‐NMR spectra were used to confirm the structures of all obtained products and they were in agreement with the proposed structure of substances. All derivatives were screened for their antioxidant activity. The most promising group was dicarboximides ( 1 – 4 , 6 ). Derivatives 2–4 displayed antioxidant activity with EC₅₀=7.75–10.89 μg/ml, which may be comparable to strong antioxidant Trolox (EC₅₀=6.13 μg/ml). Excellent activity with EC₅₀=10.75 μg/ml also presented norcantharidin analog with 1,2,4‐triazole system ( 12 ).     

Synthesis of short cationic antimicrobial peptidomimetics containing arginine analogues

Worldwide efforts are underway to develop new antimicrobial agents against bacterial resistance. To identify new compounds with a good antimicrobial profile, we designed and synthesized two series of small cationic antimicrobial peptidomimetics (1–8) containing unusual arginine mimetics (to introduce cationic charges) and several aromatic amino acids (bulky moieties to improve lipophilicity). Both series were screened for in vitro antibacterial activity against a representative panel of Gram‐positive (Staphylococcus aureus and Staphylococcus epidermidis) and Gram‐negative (Escherichia coli and Klebsiella pneumoniae) bacterial strains, and Candida albicans. The biological screening showed that peptidomimetics containing tryptophan residues are endowed with the best antimicrobial activity against S. aureus and S. epidermidis in respect to the other synthesized derivatives (MIC values range 7.5–50 µg/ml). Moreover, small antimicrobial peptidomimetics derivatives 2 and 5 showed an appreciable activity against the tested Gram‐negative bacteria and C. albicans. The most active compounds (1–2 and 5–6) have been tested against Gram‐positive established biofilm, too. Results showed that the biofilm inhibitory concentration values of these compounds were never up to 200 µg/ml. The replacement of tryptophan with phenylalanine or tyrosine resulted in considerable loss of the antibacterial action (compounds 3–4 and 7–8) against both Gram‐positive and Gram‐negative bacterial strains. Furthermore, by evaluating hemolytic activity, the synthesized compounds did not reveal cytotoxic activities, except for compound 5. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd.     

Characterization of Limonoids Isolated from the Fruits of Melia toosendan and Their Antifeedant Activity against Pieris rapae

The fruits of Melia toosendan Sieb . et Zucc . (Meliaceae) are a source of bioactive limonoids that can be used as effective pesticides. In this study, two novel limonoids, 6‐acetylsendanal and 6‐ketocinamodiol, were isolated together with fourteen known compounds, namely four protolimonoids, six trichilin‐class limonoids, and four C‐seco limonoids. The structures of the new compounds were determined by extensive spectroscopic analyses (HR‐ESI‐MS, UV, IR, 1D and 2D NMR). The bioassay results revealed that eleven of the extracted limonoids exhibited interesting antifeedant activities against the larvae of Pieris rapae with AFC₅₀ values in the range of 0.11–1.79 mm . Particularly, mesendanin H, with an AFC₅₀ value of 0.11 mm , exhibited a higher activity than the positive control toosendanin. Information on new bioactive limonoids may provide further insight into M. toosendan as a source of bioactive components.     

Antibacterial activity of naringin derivatives against pathogenic strains

Aims: To study the antimicrobial activity of naringin (NAR), a flavonoid extracted from citrus industry waste, and NAR derivatives [naringenin (NGE), prunin and alkyl prunin esters] against pathogenic bacteria such as L. monocytogenes, E. coli O157:H7 and S. aureus. The relationship between the structure of the chemical compounds and their antagonistic effect was also analysed. Methods and Results: The agar dilution technique and direct contact assaying were applied. NGE, prunin and NAR showed no antimicrobial activity at a concentration of 0·25 mmol l^?1. Similarly, fatty acids with a chain length between C2 and C18 showed no antimicrobial activity at the same concentration. However, prunin‐6″‐O‐acyl esters presented high antibacterial activity, mainly against Gram‐positive strains. This activity increased with increasing chain length (up to 10–12 carbon atoms). Alkyl prunin esters with 10–12 carbon atoms diminished viability of L. monocytogenes by about 3 log orders and S. aureus by 6 log orders after 2 h of contact at 37°C and at a concentration of 0·25 mmol l^?1. The compounds examined were not effective against any of the Gram‐negative strains assayed, even at the highest concentration. Conclusions: Addition of sugars to the aglycone did not enhance its antimicrobial activity. Attachment of a saturated aliphatic chain with 10–12 carbon atoms to the A ring of the flavonoid (or to sugars attached to this ring), seems to be the most promising modification. In conclusion, alkyl prunin esters with a chain length of C10–C12 have promising features as antimicrobial agents because of their high antilisterial and antistaphylococcal activity. Significance and Impact of the Study: This study shows that it is possible to obtain NAR derivatives with important antimicrobial activity, especially against Gram‐positive pathogenic bacteria. It also provides guidelines on the structural modifications in similar molecules to enhance the antimicrobial activity.     

A Novel Flavonoid Glucoside from Anoectochilus roxburghii （Wall,） Lindl.

Eight compounds were isolated from the ethyl acetate- and n-butanol-soluble fractions of the ethanollc extract of the whole plant of Anoectochllus roxburghll（Wali.） Lindi. （Orchidaceee）. On the basis of spectroscopic methods, the structures of these compounds were elucidated as quercetin-7-O-β-D-[6＂-O-（trans-feruloyi）]- giucopyranosids （compound 1）, 8-C-p-HydroxybenzyiquerceUn （compound 2）, isorhamnetin-7-O-β-D- giucopyranoside （compound 3）, isorhamnetin-3-O-β-D-giucopyranoside （compound 4）, kaempferoi-3-O-β-D- giucopyranoside （compound 5）, kaempferoi-7-O-β-D-giucopyranoside （compound 6）, 5-hydroxy-3＇,4＇,7- trimethoxyfiavonoi-3-O-β-D-rutinoside （compound 7）, and isorhamnetin-3-O-β-D-rutinoside （compound 8）. Of the compounds isoisted, compound 1 was a new flavonoid giucoside and exhibited strong scavenging activity against the 1,1-diphenyi-2-picryihydrazyi free radical, whereas the ethanolic extract showed weak activity. Compounds 2-8 were obtained from this family for the first time.     

Synthesis and Evaluation of 6‐Aza‐2′‐deoxyuridine Monophosphate Analogs as Inhibitors of Thymidylate Synthases,and as Substrates or Inhibitors of Thymidine Monophosphate Kinase in Mycobacterium tuberculosis

A series of 5‐substituted analogs of 6‐aza‐2′‐deoxyuridine 5′‐monophosphate, 6‐aza‐dUMP, has been synthesized and evaluated as potential inhibitors of the two mycobacterial thymidylate synthases (i.e., a flavin‐dependent thymidylate synthase, ThyX, and a classical thymidylate synthase, ThyA). Replacement of C(6) of the natural substrate dUMP by a N‐atom in 6‐aza‐dUMP 1a led to a derivative with weak ThyX inhibitory activity (33% inhibition at 50 μM ). Introduction of alkyl and aryl groups at C(5) of 1a resulted in complete loss of inhibitory activity, whereas the attachment of a 3‐(octanamido)prop‐1‐ynyl side chain in derivative 3 retained the weak level of mycobacterial ThyX inhibition (40% inhibition at 50 μM ). None of the synthesized derivatives displayed any significant inhibitory activity against mycobacterial ThyA. The compounds have also been evaluated as potential inhibitors of mycobacterial thymidine monophosphate kinase (TMPKmt). None of the derivatives showed any significant TMPKmt inhibition. However, replacement of C(6) of the natural substrate (dTMP) by a N‐atom furnished 6‐aza‐dTMP ( 1b ), which still was recognized as a substrate by TMPKmt.     

Pierisformotoxins A – D,Polyesterified Grayanane Diterpenoids from Pieris formosa and Their cAMP‐Decreasing Activities

Four highly acylated diterpenoids, designated as pierisformotoxins A–D ( 1 – 4 , resp.), along with 26 known compounds, were isolated from the flowers of Pieris formosa. Among them, pierisformotoxins A and B ( 1 and 2 , resp.) were new highly acylated grayanane diterpenoids, of which the five‐membered ring A has undergone an oxidative cleavage between C(3) and C(4), followed by lactonization, to give rise to a five‐membered lactone ring between C(3) and C(5), differing from the previously reported grayanane diterpenoids with a 5/7/6/5 ring system. Results of the cAMP‐regulation‐activity assay showed that pierisformotoxin C ( 3 ) at 10 μM (inhibitory ratio (IR): 10.1%) or 2 μM (9.8%), and pierisformotoxin B ( 2 ) at 50 μM (13.9%) significantly decreased the cAMP level in N1E‐115 neuroblastoma cells (p<0.05).     

Characterization of Cold- and High-Pressure-Active Polygalacturonases from a Deep-Sea Yeast,Cryptococcus liquefaciens Strain N6

A deep-sea yeast, Cryptococcus liquefaciens strain N6, produces two polygalacturonases, p36 and p40 (N6-PGases). These N6-PGases were highly active at 0–10 °C in comparison to a PGase from Aspergillus japonicus. The hydrolytic activity of these N6-PGases remained almost unchanged up to a hydrostatic pressure of 100 MPa at 24 °C with a very small activation volume of ?1.1 ml/mol. At 10 °C, however, the activation volume increased to 3.3 or 5.4 ml/mol (p36 and p40, respectively), suggesting that the enzyme–substrate complexes can expand at their transition states. We speculate that such a volume expansion upon forming the enzyme–substrate complexes contributes to decreasing the activation energy for hydrolysis. This can account for the high activity of N6-PGases at low-temperature.     

Chemical Constituents from Endophytic Fungus Annulohypoxylon cf. stygium in Leaves of Anoectochilus roxburghii

The chemical investigation on endophytic fungus Annulohypoxylon cf. stygium in leaves of Anoectochilus roxburghii (Wall.) Lindl . has been performed. Sixteen compounds were isolated and their structures were identified as (?)‐notoamide A, (?)‐notoamide B, (+)‐versicolamide B, notoamide C, notoamide D, stephacidin A, sterigmatocystin, dihydrosterigmatocystin, secosterigmatocystin, versiconol, averufanin, kipukasin D, kipukasin E, diorcinal, palmarumycin CP2 and (?)‐(3R)‐mellein methyl ether, respectively, by spectroscopic analysis and comparison with literature data. All the compounds were isolated from Annulohypoxylon genus for the first time. Sterigmatocystin and palmarumycin CP2 showed selective cytotoxic activities against HepG2, HeLa, MCF‐7 and HT‐29.     

Structural Characterization and α‐Glucosidase Inhibitory and Antioxidant Activities of Fucoidans Extracted from Saccharina japonica

Two sulfated fucoidan fractions (Lj3 and Lj5) were extracted from Saccharina japonica and then subjected to acid hydrolysis to obtain Lj3h and Lj5h. Lj3h and Lj5h were characterized using IR, methylation analysis, and mass spectrometry. It was found that Lj3h and Lj5h were homogeneous low molecular weight fucoidans. Specifically, Lj3h was composed of the main chain of 1,3‐linked α‐L‐fucopyranose residues with sulfate at C‐2 and/or C‐4 and three different monosaccharides (galactose, glucose, mannose) branched at C‐2 and/or C‐4 of fucose residue. Lj5h contained backbones of alternating galactopyranose residues and fucopyranose residues attached via a 1→3 linkage (galactofucan) and 1→6 linked galactan. The sulfation pattern was mainly located at C2/C4 fucose or galactose residues and more branches occupied at C‐4 of fucose residue and C‐2, C‐3 or/and C‐6 of galactose residue. In vitro assay indicated that, among the four fucoidans tested, only Lj5 showed potent α‐glucosidase inhibitory activity with IC₅₀ of 153.27±22.89 μg/mL, and the two parent fucoidans, Lj3 and Lj5, showed better antioxidant activity than their derivatives. These findings highlight the structure and bioactivity diversity of Saccharina japonica‐derived fucoidans.     

Novel Zierane‐ and Guaiane‐Type Sesquiterpenes from the Root of Melicope denhamii

Two novel zierane‐type sesquiterpenes, named melicodenones A and B ( 1 and 2 , resp.), and three new guaiane‐type sesquiterpenes, named melicodenones C–E ( 3 – 5 ), were isolated from the root of Melicope denhamii (Seem. ) T. G. Hartley together with zierone ( 6 ). Their structures were established by extensive NMR‐spectroscopic analyses. Compounds 1 – 6 were tested for cytotoxicity using human colon cancer DLD‐1 cells, and melicodenone A ( 1 ) was found to exhibit moderate activity.     

Inhibitory Effects of Constituents of an Endophytic Fungus Hypoxylon investiens on Nitric Oxide and Interleukin‐6 Production in RAW264.7 Macrophages

Three new compounds, hypoxyloamide ( 1 ), 8‐methoxynaphthalene‐1,7‐diol ( 2 ), and hypoxylonol ( 3 ), together with seven compounds isolated from nature for the first time, investiamide ( 4 ), hypoxypropanamide ( 5 ), hypoxylonol A ( 6 ), investienol ( 7 ), 2‐heptylfuran ( 8 ), (3S)‐5‐methyl‐8‐O‐methylmellein ( 9 ), (4R)‐O‐methylsclerone ( 10 ), along with 19 known compounds, 11 – 29 , were isolated from the culture broth of Hypoxylon investiens BCRC 10F0115, a fungal endophyte residing in the stems of an endemic Formosan plant Litsea akoensis var. chitouchiaoensis. The structures of the new compounds were established by spectroscopic methods, including UV, IR, HR‐ESI‐MS, and extensive 1D‐ and 2D‐NMR techniques. Of these isolates, 2 , 8‐methoxynaphthalen‐1‐ol ( 15 ), and 1,8‐dimethoxynaphthalene ( 16 ) showed nitric oxide (NO) inhibitory activity with IC₅₀ values of 11.8±0.9, 17.8±1.1, and 13.3±0.5 μM , respectively, stronger than the positive control quercetin (IC₅₀ 36.8±1.3 μM ). Compounds 2, 15 , and 16 also showed interleukin‐6 (IL‐6) inhibitory activity with IC₅₀ values of 9.2±1.7, 18.0±0.6, and 2.0±0.1 μM , stronger than the positive control quercetin (IC₅₀ 31.3±1.6 μM ). To the best of our knowledge, this is the first report on guaiane sesquiterpene metabolites, 3, 6 , and 7 , from the genus Hypoxylon.     

Synthesis of New Potential Lipophilic Co‐Drugs of 2‐Chloro‐2′‐deoxyadenosine (Cladribine, 2‐CdA,Mavenclad®, Leustatin®) and 6‐Azauridine (z6U) with Valproic Acid

2‐Chloro‐2′‐deoxyadenosine (cladribine, 1 ) was acylated with valproic acid ( 2 ) under various reaction conditions yielding 2‐chloro‐2′‐deoxy‐3′,5′‐O‐divalproyladenosine ( 3 ) as well as the 3′‐O‐ and 5′‐O‐monovalproylated derivatives, 2‐chloro‐2′‐deoxy‐3′‐O‐valproyladenosine ( 4 ) and 2‐chloro‐2′‐deoxy‐5′‐O‐valproyladenosine ( 5 ), as new co‐drugs. In addition, 6‐azauridine‐2′,3′‐O‐(ethyl levulinate) ( 8 ) was valproylated at the 5′‐OH group (→ 9 ). All products were characterized by ¹H‐ and ¹³C‐NMR spectroscopy and ESI mass spectrometry. The structure of the by‐product 6 (N‐cyclohexyl‐N‐(cyclohexylcarbamoyl)‐2‐propylpentanamide), formed upon valproylation of cladribine in the presence of N,N‐dimethylaminopyridine and dicyclohexylcarbodiimide, was analyzed by X‐ray crystallography. Cladribine as well as its valproylated co‐drugs were tested upon their cancerostatic/cancerotoxic activity in human astrocytoma/oligodendroglioma GOS‐3 cells, in rat malignant neuro ectodermal BT4Ca cells, as well as in phorbol‐12‐myristate 13‐acetate (PMA)‐differentiated human THP‐1 macrophages. The most important result of these experiments is the finding that only the 3′‐O‐valproylated derivative 4 exhibits a significant antitumor activity while the 5′‐O‐ as well as the 3′,5′‐O‐divalproylated cladribine derivatives 3 and 5 proved to be inactive.     

Volatile‐Oils Composition,and Bioactivity of the Essential Oils of Plectranthus barbatus,P. neochilus,and P. ornatus Grown in Portugal

Volatile‐oils chemical composition and bioactivity of the essentail oils from Plectranthus barbatus, P. neochilus, and P. ornatus (Lamiaceae) were assessed. Aerial parts from these three related Plectranthus species were collected from cultivated plants grown in Portugal, during vegetative and flowering phases. Volatiles, isolated by distillation? extraction, were analyzed by GC and GC/MS. Monoterpene hydrocarbons (12–74%) and sesquiterpene hydrocarbons (4–45%) constituted the main fractions in all volatiles. α‐Pinene ( 3 ; 12–67%), oct‐1‐en‐3‐ol ( 6 ; traces–28%), β‐pinene ( 7 ; 0.1–22%), and β‐caryophyllene ( 50 ; 7–12%) dominated P. barbatus volatiles. P. neochilus major volatile components were α‐terpenyl acetate ( 41 ; traces–48%), α‐thujone ( 2 ; 2–28%), β‐caryophyllene ( 50 ; 2–28%), β‐pinene ( 7 ; 1–25%), and α‐pinene ( 3 ; 1–19%). Oct‐1‐en‐3‐ol ( 6 ; 13–31%), β‐pinene ( 7 ; 11–24%), α‐pinene ( 3 ; 11–19%), and β‐caryophyllene ( 50 ; traces–11%) were the main constituents from P. ornatus volatiles. These chemical compositions were rather different from those previously found for specimens harvested in Africa and Brazil. Moreover, the volatiles from the flowers are herewith reported for the first time. Essential oils, isolated by hydrodistillation from leaves and stems, showed a yellowish color and unpleasant odor, with yields ranging from 0.08% to 0.84% (v/dry weight). Antioxidant and antimicrobial activities of the essential oils were evaluated by DPPH^. and TBARS assays, and agar disc‐diffusion method, respectively. Results showed low or moderate antioxidant capacity and significant antimicrobial activity against Gram‐positive bacteria.     

AT2R agonist NP‐6A4 mitigates aortic stiffness and proteolytic activity in mouse model of aneurysm

Clinical and experimental studies show that angiotensin II (AngII) promotes vascular pathology via activation of AngII type 1 receptors (AT1Rs). We recently reported that NP‐6A4, a selective peptide agonist for AngII type 2 receptor (AT2R), exerts protective effects on human vascular cells subjected to serum starvation or doxorubicin exposure. In this study, we investigated whether NP‐6A4–induced AT2R activation could mitigate AngII‐induced abdominal aortic aneurism (AAA) using AngII‐treated Apoe^?/? mice. Male Apoe^?/? mice were infused with AngII (1 µg/kg/min) by implanting osmotic pumps subcutaneously for 28 days. A subset of mice was pre‐treated subcutaneously with NP‐6A4 (2.5 mg/kg/day) or vehicle for 14 days prior to AngII, and treatments were continued for 28 days. NP‐6A4 significantly reduced aortic stiffness of the abdominal aorta induced by AngII as determined by ultrasound functional analyses and histochemical analyses. NP‐6A4 also increased nitric oxide bioavailability in aortic tissues and suppressed AngII‐induced increases in monocyte chemotactic protein‐1, osteopontin and proteolytic activity of the aorta. However, NP‐6A4 did not affect maximal intraluminal aortic diameter or AAA incidences significantly. These data suggest that the effects of AT2R agonist on vascular pathologies are selective, affecting the aortic stiffness and proteolytic activity without affecting the size of AAA.     

Congenic strains provide evidence that a mapped locus on chromosome 15 influences excitotoxic cell death

Inbred strains of mice differ in their susceptibility to excitotoxin‐induced cell death, but the genetic basis of individual variation is unknown. Prior studies with crosses of the FVB/NJ (seizure‐induced cell death susceptible) mouse and the seizure‐induced cell death resistant mouse, C57BL/6J, showed the presence of three quantitative trait loci (QTLs), named seizure‐induced cell death 1 (Sicd1) to Sicd3. To better localize and characterize the Sicd2 locus, two reciprocal congenic mouse strains were created. While the B6.FVB‐Sicd2 congenic mouse was without effect on modifying susceptibility to seizure‐induced excitotoxic cell death, the FVB.B6‐Sicd2 congenic mouse, in which the chromosome (Chr) 15 region of C57BL/6J was introgressed into FVB/NJ, showed reduced seizure‐induced excitotoxic cell death following kainate administration. Phenotypic comparison between FVB and the congenic FVB.B6‐Sicd2 strain confirmed that the Sicd2 interval harbors gene(s) conferring strong protection against seizure‐induced excitotoxic cell death. Interval‐specific congenic lines (ISCLs) that encompass Sicd2 on Chr 15 were generated and were used to fine‐map this QTL. Resultant progeny were treated with kainate and examined for the extent of seizure‐induced cell death in order to deduce the Sicd2 genotypes of the recombinants through linkage analysis. All of the ISCLs exhibited reduced cell death associated with the C57BL/6J phenotype; however, ISCL‐2 showed the most dramatic reduction in seizure‐induced cell death in both area CA3 and in the dentate hilus. These findings confirm the existence of polymorphic loci within the reduced critical region of Sicd2 that regulate the severity of seizure‐induced cell death.