Ryota Kirikoshi

Verruculides A and B, two new protein tyrosine phosphatase 1B inhibitors from an Indonesian ascidian-derived Penicillium verruculosum.

Two new merosesquiterpenes, verruculides A (1) and B (2), were isolated from a culture broth of the Indonesian ascidian-derived Penicillium verruculosum TPU1311, together with three known congeners, chrodrimanins A (3), B (4), and H (5). The structures of 1 and 2 were assigned on the basis of their spectroscopic data (1D and 2D NMR, HRMS, UV, CD, and IR). Compound 2 had a linear sesquiterpene moiety and was considered to be the derivative of the biosynthetic precursor for 1 and 3-5. Compounds 1, 3, and 5 inhibited the activity of protein tyrosine phosphatase 1B (PTP1B) with IC50 values of 8.4, 8.5, and 14.9 μM, respectively. Compound 2 showed 40% inhibition at 23.1 μM, while 4 was not active at 20.7 μM.

Structures and Biological Evaluations of Agelasines Isolated from the Okinawan Marine Sponge Agelas nakamurai.

Three new N-methyladenine-containing diterpenes, 2-oxoagelasines A (1) and F (2) and 10-hydro-9-hydroxyagelasine F (3), were isolated from the Okinawan marine sponge Agelas nakamurai Hoshino together with eight known agelasine derivatives, 2-oxoagelasine B (4), agelasines A (5), B (6), D (7), E (8), F (9), and G (10), and ageline B (11). The structures of 1-3 were assigned on the basis of their spectroscopic data and their comparison with those of the literature. Compounds 3 and 5-11 inhibited the growth of Mycobacterium smegmatis with inhibition zones of 10, 14, 15, 18, 14, 20, 12, and 12 mm at 20 μg/disc, respectively. All compounds were inactive (IC50 > 10 μM) against Huh-7 (hepatoma) and EJ-1 (bladder carcinoma) human cancer cell lines. Three 2-oxo derivatives (1, 2, and 4) exhibited markedly reduced biological activity against M. smegmatis. Moreover, compound 10 inhibited protein tyrosine phosphatase 1B (PTP1B) activity with an IC50 value of 15 μM.

Two new protein tyrosine phosphatase 1B inhibitors, hyattellactones A and B, from the Indonesian marine sponge Hyattella sp.

Two unique sesterterpenes, hyattellactones A (1) and B (2), together with two known sesterterpenes, phyllofolactones F (3) and G (4), were isolated from the Indonesian marine sponge Hyattella sp. The structures of the two new compounds, 1 and 2 were assigned based on their spectroscopic data. Hyattellactone A (1) was a scalarane sesterterpene with an α,β-unsaturated-γ-lactone ring and C-ethyl group, while B (2) was an epimer of 1 at the C-24 position. Compounds 1 and 3 inhibited PTP1B activity with IC50 values of 7.45 and 7.47μM, respectively. On the other hand, compounds 2 and 4 (24S-isomers of 1 and 3, respectively) showed much reduced activity than the 24R-isomers.

Strongylophorines, new protein tyrosine phosphatase 1B inhibitors, from the marine sponge Strongylophora strongilata collected at Iriomote Island.

A new meroditerpene, 26-O-ethylstrongylophorine-14 (1), was isolated from the Okinawan marine sponge Strongylophora strongilata together with six known strongylophorines: 26-O-methylstrongylophorine-16 (2) and strongylophorines-2 (3), -3 (4), -8 (5), -15 (6), and -17 (7). The structure of 1 was assigned on the basis of its spectroscopic data. Compound 1 inhibited the activity of protein tyrosine phosphatase 1B (PTP1B) with an IC50 value of 8.7 μM, while known compounds 2-8 gave IC50 values of 8.5, >24.4, 9.0, 21.2, 11.9, and 14.8 μM, respectively. Oleanolic acid, a positive control, inhibited PTP1B activity at 0.7 μM (IC50). The inhibitory activities of strongylophorines possessing the acetal moiety at C-26 (1, 2, and 6) were stronger than those of the lactone derivatives (3 and 5). This is the first study to demonstrate that meroditerpenes inhibit PTP1B activity.

Roles of Intramolecular and Intermolecular Hydrogen Bonding in a Three-Water-Assisted Mechanism of Succinimide Formation from Aspartic Acid Residues

Aspartic acid (Asp) residues in peptides and proteins are prone to isomerization to the β-form and racemization via a five-membered succinimide intermediate. These nonenzymatic reactions have relevance to aging and age-related diseases. In this paper, we report a three water molecule-assisted, six-step mechanism for the formation of succinimide from Asp residues found by density functional theory calculations. The first two steps constitute a stepwise iminolization of the C-terminal amide group. This iminolization involves a quintuple proton transfer along intramolecular and intermolecular hydrogen bonds formed by the C-terminal amide group, the side-chain carboxyl group, and the three water molecules. After a conformational change (which breaks the intramolecular hydrogen bond involving the iminol nitrogen) and a reorganization of water molecules, the iminol nitrogen nucleophilically attacks the carboxyl carbon of the Asp side chain to form a five-membered ring. This cyclization is accompanied by a triple proton transfer involving two water molecules, so that a gem-diol tetrahedral intermediate is formed. The last step is dehydration of the gem-diol group catalyzed by one water molecule, and this is the rate-determining step. The calculated overall activation barrier (26.7 kcal mol−1) agrees well with an experimental activation energy.

Trichoketides A and B, two new protein tyrosine phosphatase 1B inhibitors from the marine-derived fungus Trichoderma sp.

Two new octaketides, trichoketides A (1) and B (2), were isolated from a culture broth of the seawater-derived fungus Trichoderma sp. TPU1237 together with two known analogs, trichodermaketones C (3) and D (4), by ODS column chromatography followed by preparative ODS and chiral HPLC. The structures of 1 and 2 were elucidated on the basis of their spectroscopic data, and absolute configurations were assigned by comparing their experimental electronic circular dichroism (ECD) spectra with the calculated ECD spectra. Compounds 1 and 2 were epimers at the C-8 position (α-position of dihydrofuran ring). The IC50 values of compounds 1–4 against protein tyrosine phosphatase 1B were 53.1, 65.1, 68.0 and 55.9 μM, respectively.

Penicyrones A and B, an epimeric pair of α-pyrone-type polyketides produced by the marine-derived Penicillium sp.

Two polyketides containing an α-pyrone unit, named penicyrones A (1) and B (2), were isolated from a culture broth of the marine-derived Penicillium sp. TPU1271 together with nine known compounds: verrucosidin (3), fructigenine A (4), verrucofortine (5), cyclo-(L-Trp-L-Phe) (6), cyclopenol (7), cyclopenin (8), penipratynolene (9), aspterric acid (10) and viridicatol (11). The structures of 1 and 2 were elucidated by analyzing the spectroscopic data of 1, 2 and their O-acetyl derivatives (1a and 2a). Compounds 1 and 2 were epimers of each other at the C-9 position. The absolute configurations of 1 and 2 were assigned on the basis of NOESY data for 1, 2, 1a and 2a, a conformational analysis and the identity of the biogenetic pathway with verrucosidin (3). The planar structure of penicyrones was found in the SciFinder as a compound in the commercial chemical libraries; however, the stereostructure and spectroscopic data were not available. Therefore, this is the first study on the isolation and structure elucidation, including the absolute configurations, of penicyrones A (1) and B (2) as fungal metabolites. Compound 3 exhibited growth inhibitory activity against Mycobacterium smegmatis at 40 μg per disc (inhibition zone of 11 mm). This is the first study to demonstrate that verrucosidin (3) exhibited anti-mycobacterial activity.

Haliclonadiamine Derivatives and 6-epi-Monanchorin from the Marine Sponge Halichondria panicea Collected at Iriomote Island

Four new haliclonadiamine analogues, (10Z,12E)-haliclonadiamine (1), (10E,12Z)-haliclonadiamine (2), and halichondriamines A (3) and B (4), were isolated from the Okinawan marine sponge Halichondria panicea together with haliclonadiamine (5) and papuamine (6). The structures of 1-4 were elucidated on the basis of their spectroscopic data by comparisons with those for 5 and 6. Further separation of the remaining fraction led to the isolation of a new bicyclic guanidine alkaloid, 6-epi-monanchorin (7), along with monanchorin (8). Compound 7 is the epimer of 8 at the 6 position. Compounds 1-6 inhibited the growth of Mycobacterium smegmatis with inhibition zones of 12, 7, 8, 7, 16, and 12 mm at 10 μg/disc, respectively. Compounds 2-4 exhibited weak cytotoxicities against the Huh-7 (hepatoma) human cancer cell line and were 2-fold less active than 5 and 6. Compounds 7 and 8 were not active against M. smegmatis at 20 μg/disc or the cancer cell line at 10 μM.

Racemization of the Succinimide Intermediate Formed in Proteins and Peptides: A Computational Study of the Mechanism Catalyzed by Dihydrogen Phosphate Ion

In proteins and peptides, d-aspartic acid (d-Asp) and d-β-Asp residues can be spontaneously formed via racemization of the succinimide intermediate formed from l-Asp and l-asparagine (l-Asn) residues. These biologically uncommon amino acid residues are known to have relevance to aging and pathologies. Although nonenzymatic, the succinimide racemization will not occur without a catalyst at room or biological temperature. In the present study, we computationally investigated the mechanism of succinimide racemization catalyzed by dihydrogen phosphate ion, H2PO4−, by B3LYP/6-31+G(d,p) density functional theory calculations, using a model compound in which an aminosuccinyl (Asu) residue is capped with acetyl (Ace) and NCH3 (Nme) groups on the N- and C-termini, respectively (Ace–Asu–Nme). It was shown that an H2PO4− ion can catalyze the enolization of the Hα–Cα–C=O portion of the Asu residue by acting as a proton-transfer mediator. The resulting complex between the enol form and H2PO4− corresponds to a very flat intermediate region on the potential energy surface lying between the initial reactant complex and its mirror-image geometry. The calculated activation barrier (18.8 kcal·mol−1 after corrections for the zero-point energy and the Gibbs energy of hydration) for the enolization was consistent with the experimental activation energies of Asp racemization.

Isopetrosynol, a New Protein Tyrosine Phosphatase 1B Inhibitor, from the Marine Sponge Halichondria cf. panicea Collected at Iriomote Island

A new polyacetylene compound, isopetrosynol (1), was isolated from the Okinawan marine sponge Halichondria cf. panicea together with petrosynol (2), adociacetylene D (3), (5R)-3,15,27-triacontatriene-1,29-diyn-5-ol (4), and petrosterol (5). The structure of 1 was assigned on the basis of spectroscopic data for 1 and 2. Compound 1 inhibited protein tyrosine phosphatase 1B (PTP1B) activity with an IC50 value of 8.2±0.3 µM, while compound 2, a diastereomer of 1, showed only 28.9±4.5% inhibition at 21.6 µM. The IC50 values of compounds 3 and 4 were 7.8±0.5 and 12.2±0.5 µM, respectively. Oleanolic acid, a positive control, inhibited PTP1B activity at 0.7±0.1 µM (IC50) in the same experiment. The inhibitory activity of 1 was stronger than that of its diastereomer (2). This is the first study to show the inhibitory effects of polyacetylene compounds on PTP1B.