Yoshihito Inai

Chain-Terminus Triggered Chiral Memory in an Optically Inactive 310-Helical Peptide

A new optically inactive 3(10)-helical peptide with a side-chain cross-linking was found to exhibit chiral memory stored in the peptide backbone, whose chirality was induced by a noncovalent interaction of a chiral molecule at the N-terminal end of the peptide.

Accelerated biodegradation of poly(vinyl alcohol) by a glycosidation of the hydroxyl groups

Abstract Biodegradability of N-acetyl- d -glucosamine (GlcNAc)-substituted poly(vinyl alcohol) (PVA) (1) in a soil suspension (pH 6.5) was investigated at 25°C for 40 days. Biochemical oxygen demand (BOD) of 1 with degree of substitution of 0.2–0.3 (DP=430–480) was higher than that of PVA under the degradation condition. Size exclusion chromatography (SEC), 1H NMR, and FT-IR measurements of the recovered sample indicated that biodegradation of PVA main chain was accelerated by partial glycosidation of hydroxyl groups in PVA.

Terminal effect of chiral residue on helical screw sense in achiral peptides

To understand the terminal effect of chiral residue for determining a helical screw sense, we adopted five kinds of peptides I–V containing N- and/or C-terminal chiral Leu residue(s): Boc–L-Leu–(Aib–ΔPhe)2–Aib–OMe (I), Boc–(Aib–ΔPhe)2–L-Leu–OMe (II), Boc–L-Leu–(Aib–ΔPhe)2–L-Leu–OMe (III), Boc–D-Leu–(Aib–ΔPhe)2–L-Leu–OMe (IV), and Boc–D-Leu–(Aib–ΔPhe)2–Aib–OMe (V). The segment –(Aib–ΔPhe)2– was used for a backbone composed of two “enantiomeric” (left-/right-handed) helices. Actually, this could be confirmed by 1H-nmr [nuclear Overhauser effect (NOE) and solvent accessibility of NH resonances] and CD spectroscopy on Boc–(Aib–ΔPhe)2–Aib–OMe, which took a left-/right-handed 310-helix. Peptides I–V were also found to take 310-type helical conformations in CDCl3, from difference NOE measurement and solvent accessibility of NH resonances. Chloroform, acetonitrile, methanol, and tetrahydrofuran were used for CD measurement. The CD spectra of peptides I–III in all solvents showed marked exciton couplets with a positive peak at longer wavelengths, indicating that their main chains prefer a left-handed screw sense over a right-handed one. Peptide V in all solvents showed exciton couplets with a negative peak at longer wavelengths, indicating it prefers a right-handed screw sense. Peptide IV in chloroform showed a nonsplit type CD pattern having only a small negative signal around 280 nm, meaning that left- and right-handed helices should exist with almost the same content. In the other solvents, peptide IV showed exciton couplets with a negative peak at longer wavelengths, corresponding to a right-handed screw sense. From conformational energy calculation and the above 1H-nmr studies, an N- or C-terminal L-Leu residue in the lowest energy left-handed 310-helical conformation was found to take an irregular conformation that deviates from a left-handed helix. The positional effect of the L-residue on helical screw sense was discussed based on CD data of peptides I–V and of Boc–(L-Leu–ΔPhe)n–L-Leu–OMe (n = 2 and 3).

Chemical modification of hydroxyl groups of poly(vinyl alcohol) by a glycosidation reaction

A new procedure for chemical modification of poly(vinyl alcohol) (PVA) was established by a glycosidation reaction of hydroxyl groups in PVA with triacetylated sugar oxazoline 1. 1 H and 13 C NMR analyses indicated that triacetylated N-acetyl-D-glucosamine (GlcNAc) was introduced onto a PVA backbone selectively via a β-O-glycoside linkage. Deacetylation of triacetylated GlcNAc-substituted PVA 2 resulted in GlcNAc-substituted PVA 3 in good yield. These modified PVAs 2 and 3 exhibited solubilities and thermal properties different from the original PVA.

Screw sense preference of non-polar L-amino acid residues second from the N-terminal position

To understand the positional effects of a single chiral residue on the helical screw sense of an achiral segment, we adopted five kinds of peptides Boc-Aib-X*-(Aib-ΔZPhe)2-Aib-OMe (Boc, t-butoxycarbonyl; Aib, α-aminoisobutyric acid; ΔZPhe, (Z)-dehydrophenylalanine; OMe, methoxy), wherein the X* residue is an L-residue of leucine (Leu), alanine (Ala), valine (Val), phenylalanine (Phe), or 1-naphthylalanine (Nap). Here the segment -(Aib-ΔZPhe)2-Aib-OMe was employed as an achiral backbone for generating two “enantiomeric” (left-handed/right-handed) helices. All of the peptides are folded into a 310-type helical conformation in chloroform, as evidenced by FT-IR and 1H NMR techniques. A CD analysis of these peptides indicates that they adopt both left-handed and right-handed helices, and that the prevailing screw sense as well as the screw sense bias depend on the type of solvent. Thus, the L-residue located at the position second from the N-terminus plays a unique role for energetically permitting both helices. These peptides also undergo a solvent-induced interconversion between both helices. The rank order of the penultimate L-residues for inducing a right-handed screw sense is Val > Leu ∼ Ala > Phe > Nap, of which the reverse order represents the tendency to promote a left-handed screw sense. The prevailing screw sense induced by the penultimate L-residue is also discussed on the basis of conformational energy calculations. In conclusion, we here have been able to express experimentally a unique screw sense preference of these non-polar L-amino acids.

Equivalent cross-relaxation rate imaging in the synthetic copolymer gels and invasive ductal carcinomas of the breast

The values of equivalent cross-relaxation rate (ECR) correlated well with [i] water conditions in various copolymer gels and [ii] nature of malignant cells with regard to nuclear dysplasia and mitotic potential in breast carcinomas. The synthetic copolymer gels composed of any two or three monomers among 2-hydroxyethyl methacrylate (HEMA), glycidyl methacrylate (GMA), N-vinyl-2-pyrrolidinone (N-VP), methyl methacrylate (MMA) and benzyl methacrylate (BMA). The ECR measurement was performed by using an off-resonance saturation pulse under conventional field-echo imaging at frequency within +/- 75 ppm apart from the water resonance frequency. The ECR values were readily to determine and non-time consuming parameter for cross relaxation rate. The ECR values at the frequency offset by 7-ppm (ECR-7) were divided the sample gels two classes, which must correspond to hydrophilic or hydrophobic ones. The sensitivity in the gels was nearly equivalent to the cross-relaxation rate itself. In the breast carcinomas, the ECR-7 correlates with the nature of malignant cells with regard to nuclear dysplasia and mitotic potential. The ECR-7 is better or more accurate than the STR-7 because the SDNRs between carcinoma and glandular tissue increased by approximately 50% on the ECR-7 compared with the STR-7. Thus the ECR values could be a new parameter for malignancy and cell proliferative activity of the breast carcinomas with non-invasive modalities by magnetic resonance imaging.

Synthesis of ΔEPhe‐containing tripeptide via photoisomerization and its conformation in solution

A new synthetic route to (E)-beta-phenyl-alpha,beta-dehydroalanine (delta(E)Phe)-containing peptide was presented via photochemical isomerization of the corresponding (Z)-beta-phenyl-alpha,beta-dehydroalanine (delta(Z)Phe)-containing peptide. By applying this method to Boc-Ala-delta(Z)Phe-Val-OMe (Z-I: Boc, t-butoxycarbonyl; OMe, methoxy), Boc-Ala-delta(E)Phe-Val-OMe (E-I) was obtained. The identification of peptide E-I was evidenced by 1H-nmr, 13C-nmr, and uv absorption spectroscopy, elemental analysis, and hydrogenation. The conformation of peptide E-I in CDCl3 was investigated by 1H-nmr spectroscopy (solvent dependence of NH chemical shift and difference nuclear Overhauser effect). Interestingly, peptide E-I differed from peptide Z-I in the hydrogen-bonding mode. Namely, for peptide Z-I, only Val NH participates in intramolecular hydrogen bonding, which leads to a type II beta-turn conformation supported by hydrogen bonding between CO(Boc) and NH(Val). On the other hand, for peptide E-I, two NHs, delta(E)Phe NH and Val NH, participate in intramolecular hydrogen bonding. In both peptides, a remarkable NOE (approximately 11-13%) was observed for Ala C(alpha) H-deltaPhe NH pair. Based on the nmr data and conformational energy calculation, it should be concluded that peptide E-I takes two consecutive gamma-turn conformations supported by hydrogen bonding between CO(Boc) and NH(delta(E)Phe), and between CO(Ala) and NH(Val) as its plausible conformation.

Ordered nanopattern arrangement of gold nanoparticles on β-sheet peptide templates through nucleobase pairing.

We have demonstrated a unique method for rational arrangement of gold (Au) nanoparticles on a β-sheet peptide template through nucleobase pairing. For the template, the 16-mer peptide 1 was synthesized, which is based on an alternating amphiphilic sequence of Asp-Leu. Here Leu at the sixth position is replaced by thymine-modified Lys, and a polyethylene glycol chain is introduced to the C-terminus. The surface of Au nanoparticles was modified with the complementary adenyl group. Peptide 1 formed a stable β-sheet monolayer at the air/water interface under an appropriate surface pressure. The monolayer film transferred onto a mica surface by the Langmuir-Blodgett method showed a linearly striped pattern with 6.1 nm average stripe width and 6 nm average interval between stripes, derived from β-sheet assembly. The adenine-bound Au nanoparticles were successfully immobilized on the thymine-bound template through a complementary adenine-thymine hydrogen bonding pair. Interestingly, linear assembly structures of the Au nanoparticles were observed, thus being successfully reproduced by the original striped pattern of the template of 1. Our method might readily fabricate Au materials with our desirable 2D pattern through fine-tuning of β-sheet sequence and nucleobase position.

Synthesis and Helical Structures of Poly(ω‐alkynamide)s Having Chiral Side Chains: Effect of Solvent on Their Screw‐Sense Inversion

New ω-alkynamides, (S)-HC≡CCH2CONHCH2CH(CH3)CH2CH3 (1) and (S)-HC≡CCH2CH2CONHCH(CH3)CH2CH2CH2CH2CH3 (2) were synthesized and polymerized with a rhodium catalyst in CHCl3 to obtain cis-stereoregular poly(ω-alkynamide)s (poly(1) and poly(2)). Polarimetric, CD, and IR spectroscopic studies revealed that in solution the polymers adopted predominantly one-handed helical structures stabilized by intramolecular hydrogen bonds between the pendent amide groups. This behavior was similar to that of the corresponding poly(N-alkynylamide) counterparts (poly(3) and poly(4)) reported previously, whereas the helical senses were opposite to each other. The helical structures of the poly(ω-alkynamide)s were stable upon heating similar to those of the poly(N-alkynylamide)s, but the solvent response was completely different. An increase in MeOH content in CHCl3/MeOH resulted in inversion of the predominant screw-sense for poly(1) and poly(2). Conversely, poly(3) was transformed into a random coil, and poly(4) maintained the predominant screw-sense irrespective of MeOH content. The solvent dependence of predominant screw-sense for poly(1) and poly(2) was reasonably explained by molecular orbital studies using the conductor-like screening model (COSMO).

Structural and conformational properties of (Z)-?-(1-naphthyl)- dehydroalanine residue

To understand how chemical structure of beta-substituted alpha, beta-dehydroalanine (particularly size and pi conjugation of beta substituent) affects conformational property, x-ray crystallographic analysis was performed on Boc-Ala-Delta(Z) Nap-Val-OMe [Boc: t-butoxycarbonyl; Delta(Z) Nap: (Z)-beta-(1-naphthyl)dehydroalanine; OMe: methoxy] having the naphthyl group as a bulky beta substituent. Single crystals were grown by slow evaporation from an ethanol solution in the triclinic space group P1 with a = 9.528 (3) A, b = 12.410(4) A, c = 5.975(2) A, alpha = 96.77(3) degrees, beta = 102. 81(2) degrees, gamma = 88.74(3) degrees, V = 684.1(4) A3, and Z = 1. Phase determination was carried out by a direct method (SHELEXS), and the final structure was refined to R = 8.1% and R(w) = 9.0% for 1964 observed reflections. The bond lengths and bond angles of the Delta(Z)Nap residue, characterized by a sp(2) hybridized C(alpha) atom, did not differ from those of other dehydroresidues such as Delta(Z) Phe, Delta(Z) Leu, and DeltaVal essentially. The peptide backbone took a type II beta-turn conformation involving an intramolecular hydrogen bond between CO(Boc) and NH(Val), similar to di- or tripeptides containing a Delta(Z) Phe or Delta(Z) Leu residue in the second positions. Here the naphthyl group was found to be nonplanar [chi(2) = 55(1) degrees ] relative to the C(alpha)==C(beta)==C(gamma) plane. The nonplanarity was supported by conformational energy calculation. The molecular packing was stabilized by two kinds of intermolecular hydrogen bonds and van der Waals interactions. Naphthyl groups were arranged in a partially overlapped face-to-face orientation with a center-to-center distance of 5.97 A. For additional information, peptide Boc-(Ala-Delta(Z) Nap-Leu)(2)-OMe was synthesized and its solution conformation was investigated by (1)H-NMR spectroscopy. The hexapeptide showed the tendency to form a 3(10)-helical conformation in solution essentially. Conformational properties of Delta(Z) Nap residue, characterized by a type II beta-turn and 3(10)-helix, were supported by a conformational energy contour map of the Delta(Z)Nap residue.