Search

Salusin-β has been detected in numerous mammalian tissues and has been shown to have various effects on the cardiovascular system. In this study, we showed that salusin-β exhibited potent antibacterial activity against Gram-positive microorganisms such as Bacillus subtilis NBRC 3513, Bacillus megaterium ATCC 19213, Staphylococcus aureus NBRC 12732, and Staphylococcus epidermidis NBRC 12933. A cytoplasmic membrane-depolarizing assay using the DiSC3(5) dye revealed that the addition of 4 nmol/mL of salusin-β caused the leakage of fluorescence dye from Staphylococcus aureus NBRC 12732. The antimicrobial potency and circular dichroism (CD) spectroscopy of five analogs related to salusin-β were examined to determine structure-function relationships in its N- and C-terminal regions. The results obtained suggest that the N-terminal sequences of the salusin-β molecule are important for the expression of the potent antimicrobial activity of this peptide. A profile corresponding to that of the α-helix conformation was observed in the salusin-β solution.

The activity of cis-cinnamic acid (cis-CA), one of the allelochemicals, in plants is very similar to that of indole-3-acetic acid (IAA), a natural auxin, and thus cis-CA has long been believed to be an analog of auxin. We have reported some structure-activity relationships studies by synthesizing over 250 cis-CA derivatives and estimating their inhibitory activities on root growth inhibition in lettuce. In this study, the compounds that showed low- or no-activity on root growth inhibition were recruited as candidates suppressors against cis-CA and/or auxin and tested for their activity. In the presence of cis-CA, lettuce root growth was inhibited; however, the addition of some cis-CA derivatives restored control-level root growth. Four compounds, (Z)-3-(4-isopropylphenyl)acrylic acid, (Z)-3-(3-butoxyphenyl)acrylic acid, (Z)-3-[3-(pentyloxy)phenyl]acrylic acid, and (Z)-3-(naphthalen-1-yl)acrylic acid were selected as candidates for a cis-CA selective suppressor they allowed the recovery of root growth from inhibition by cis-CA treatment without any effects on the IAA-induced effect or elongating activity by themselves. Three candidates significantly ameliorated the root shortening by the potent inhibitor derived from cis-CA. In brief, we have found some cis-CA selective suppressors which have never been reported from inactive cis-CA derivatives for root growth inhibition. cis-CA selective suppressors will play an important role in elucidating the mechanism of plant growth regulation.

To find candidates with high antimicrobial and low hemolytic activities, many gratisin (GR) analogues have been designed and synthesized. In the present account, we synthesized novel derivatives of GR having both the polycationic and fatty acyl groups, cyclo{-Val(1)-Orn(2)-Leu(3)-D-Phe(4)-Pro(5)-D-Lys(6)(X)-Val(7)-Orn(8)-Leu(9)-D-Phe(10)-Pro(11)-D-Lys(12)-} {X=-CO(CH(2))(6)CH(3) (1), -Lys-CO(CH(2))(6)CH(3) (2), -(Lys)(2)-CO(CH(2))(6)CH(3) (3), and -(Lys)(3)-CO(CH(2))(6)CH(3) (4)}, and examined the biological activities. Among them, we found that 2-4 have differential ionic interaction against the prokaryotic membrane and eukaryotic membrane. In other words, the dissociation with high antimicrobial activity and low hemolytic activity is caused by the addition of D-Lys(6)-{(Lys)(n)-CO(CH(2))(6)CH(3)} residues at position 6 of [D-Lys(6,12)]-GR. Our findings should be helpful in finding drug candidates with high antimicrobial activity and low hemolytic activity that are capable of combating microbial resistance.

The substitution of each constituent amino acid residue of gramicidin S (GS), cyclo(-Val(1,1')-Orn(2,2')-Leu(3,3')-D-Phe(4,4')-Pro(5,5')-)(2) with Lys residue indicated that each side chain structure of the constituent amino acid residues affect largely the antibiotic activity and hemolytic activity of GS. Further, the substitution of D-Phe(4,4') and Pro(5,5') residues with basic amino acid residues as a Lys residue results the high antibiotic activity and the very low hemolytic activity. Thus, we have found novel positions on the scaffold of GS at D-Phe(4,4') and Pro(5,5') residues whose modification will significantly increase the therapeutic index.

Polymyxin B (PMB) is a cationic cyclic decapeptide antibiotic with a fatty acyl (FA) modification at the α-amino group of Dab¹ (Dab: L-α,γ-diaminobutyric acid). In this study, which is part of a series of PMB structure-activity relationship investigations focused on identifying clinically useful peptide antibiotics, we synthesized ten des-FA PMB derivatives whose N-terminal moieties were changed to basic or hydrophilic amino acids. The antimicrobial and lipopolysaccharide (LPS) binding activities of these synthetic analogs were tested. The analogs showed more potent antimicrobial activity against Pseudomonas aeruginosa (P. aeruginosa) compared with the PMB nonapeptide. In particular, [Ser²-Dap³]-PMB(2-10), Guanyl-[Thr²-Dab³]-PMB(2-10), Guanyl-[Dab¹-Thr²-Dab³]-PMB(1-10), and N(α,γ)-diguanyl-[Dap³]-PMB(3-10) had antimicrobial activity equivalent to PMB. In LPS binding assays, the displacement curves shifted in a manner proportional to the number of positive charges available to bind to Escherichia coli (E. coli) and P. aeruginosa. Furthermore, peptides with basic side chains were comparable to PMB in binding activity assays against E. coli and P. aeruginosa. The acute toxicities of the peptides were evaluated by intravenously administering the peptides to mice through the tail vein. The toxicities of [Ser²-Dap³]-PMB(2-10), [Dap³]-PMB(3-10), and [Ser³]-PMB(3-10) were lower that of PMB (LD₅₀, 4.8 µmol/kg).

To find candidates with high antimicrobial and low hemolytic activities, many gramicidin S (GS) analogs of various ring sizes have been designed and synthesized. However, syntheses of antimicrobially active analogues of GS having a disordered symmetry structure from C(2) have almost never been reported, because the stable, amphiphilic β-sheet structure of GS with C(2) symmetry is considered essential for its strong antibacterial activity. In the present studies, novel thirteen cycloundecapeptides 1-13 related to GS were synthesized and examined. Among them, cyclo(-Va1(1)-Orn(2)-Leu(3)-D-Phe(4)-X(5)-Pro(6)-Val(7)-Orn(8)-Leu(9)-D-Phe(10)-Pro(11)-) (X=Lys (10), Orn (11), Arg (12) and Lys(Lys) (13)) resulted in high antibiotic activity against both Gram-positive and Gram-negative microorganisms tested. In addition, 11 showed low toxicity against sheep blood cells compared with that of GS. Further, circular dichroism (CD) spectra of 10-13 had a curve similar to each other, suggesting that the conformations of these analogues in methanol are similar to each other. However, CD spectra of 10-13 were different from that of GS in the 190-210 nm region. These results suggest that the presences of one added amino acid residue at position 5 of 10-13 might be partially effective through a structural change in the biological activity of 10-13. In addition, the structural modifications at position 5 lower the undesirable hemolytic activity and enhance the desirable antibiotic activity.

Two ways for the synthesis of binaphthyl were examined based on a chiral ligand-mediated asymmetric conjugate addition of 1-naphthyllithium to naththalene-2-carboxylic acid 2,6-di-t-butyl-4-methoxyphenyl esters. The one pot method by conjugate addition-elimination gave a relatively higher enantioselectivity than the two step synthesis based on addition and subsequent oxidative aromatization.

This study on the structure-activity relationship of polymyxin B, a cyclic peptide antibiotic, used sixteen synthetic polymyxin B(3) analogs including alanine scanning analogs to elucidate the contribution of the side chains to antimicrobial activity and lipopolysaccharide (LPS) binding. Of these analogs, [Ala(5)]-polymyxin B(3) showed greatly reduced antimicrobial activity against Escherichia coli (E. coli), Salmonella Typhimurium (S. Typhimurium) and Pseudomonas aeruginosa (P. aeruginosa) with MIC values of 4-16 nmol/ml, suggesting that the Dab (alpha,gamma-diaminobutyric acid) residue at position 5 is the most important residue contributing to bactericidal activity. The antibacterial contribution of Dab when located within the lactam ring (positions 5, 8 and 9) was greater than when located outside the ring (positions 1 and 3). [D-Ala(6)]-, [L-Phe(6)]-, [Ala(7)]-, and [Gly(7)]-polymyxin B(3) analogs retained potent antimicrobial activity, indicating that neither the reduction of hydrophobic character of the D-Phe(6)-Leu(7) region nor the D-configuration at position 6 is indispensable for antimicrobial activity. LPS binding studies showed that decreased hydrophobicity of the lactam ring had little effect, but the N(gamma)-amino function of the Dab residues at position 1, 3, 5, 8 and 9 greatly affected LPS binding, with the contribution of Dab(5) being the most significant.

Aliphatic alpha,alpha-dibromo esters, precursors of ynolates, were synthesized via bromination of lithium alpha-bromo ester enolates with 1,2-dibromotetrafluoroethane in good yields. alpha-Trimethylsilyl-alpha,alpha-dibromo esters were synthesized via radical bromination.

The reactions of the lithium enolate of 1-tetralone with reactive alkyl halides were examined in the absence and in the presence of 3 eq of various ligands for the lithium. It is shown that the rates of the reactions are enhanced greatly in the presence a tetradentate amine (1,1,4,7,10,10-hexamethyltriethylenetetramine), and the ratio of the monoalkylated product to the dialkylated product is increased under shorter reaction times.