Cyclic isoDGR and RGD Peptidomimetics Containing Bifunctional Diketopiperazine Scaffolds are Integrin Antagonists

The cyclo[DKP‐isoDGR] peptidomimetics 2 – 5 , containing bifunctional diketopiperazine (DKP) scaffolds that differ in the configuration of the two DKP stereocenters and in the substitution at the DKP nitrogen atoms, were prepared and examined in vitro in competitive binding assays with purified α_vβ₃ and α_vβ₅ integrin receptors. IC₅₀ values ranged from low nanomolar (ligand 3 ) to submicromolar with α_vβ₃ integrin. The biological activities of ligands cyclo[DKP3‐RGD] 1 and cyclo[DKP3‐isoDGR] 3 , bearing the same bifunctional DKP scaffold and showing similar α_Vβ₃ integrin binding values, were compared in terms of their cellular effects in human U373 glioblastoma cells. Compounds 1 and 3 displayed overlapping inhibitory effects on the FAK/Akt integrin activated transduction pathway and on integrin‐mediated cell infiltration processes, and qualify therefore, despite the different RGD and isoDGR sequences, as integrin antagonists. Both compounds induced apoptosis in glioma cells after 72 hour treatment.     

Synthesis and Biological Evaluation of RGD Peptidomimetic–Paclitaxel Conjugates Bearing Lysosomally Cleavable Linkers

Two small‐molecule–drug conjugates (SMDCs, 6 and 7 ) featuring lysosomally cleavable linkers (namely the Val–Ala and Phe–Lys peptide sequences) were synthesized by conjugation of the α_vβ₃‐integrin ligand cyclo[DKP–RGD]‐CH₂NH₂ ( 2 ) to the anticancer drug paclitaxel (PTX). A third cyclo[DKP–RGD]–PTX conjugate with a nonpeptide “uncleavable” linker ( 8 ) was also synthesized to be tested as a negative control. These three SMDCs were able to inhibit biotinylated vitronectin binding to the purified α_Vβ₃‐integrin receptor at nanomolar concentrations and showed good stability at pH 7.4 and pH 5.5. Cleavage of the two peptide linkers was observed in the presence of lysosomal enzymes, whereas conjugate 8 , which possesses a nonpeptide “uncleavable” linker, remained intact under these conditions. The antiproliferative activities of the conjugates were evaluated against two isogenic cell lines expressing the integrin receptor at different levels: the acute lymphoblastic leukemia cell line CCRF‐CEM (α_Vβ₃?) and its subclone CCRF‐CEM α_Vβ₃ (α_Vβ₃+). Fairly effective integrin targeting was displayed by the cyclo[DKP–RGD]–Val–Ala–PTX conjugate ( 6 ), which was found to differentially inhibit proliferation in antigen‐positive CCRF‐CEM α_Vβ₃ versus antigen‐negative isogenic CCRF‐CEM cells. The total lack of activity displayed by the “uncleavable” cyclo[DKP–RGD]–PTX conjugate ( 8 ) clearly demonstrates the importance of the peptide linker for achieving the selective release of the cytotoxic payload.     

Xanthones with α‐Glucosidase Inhibitory Activities from Aspergillus versicolor,a Fungal Endophyte of Huperzia serrata

Three new xanthones, namely huperxanthones A–C ( 1 – 3 , resp.), were obtained from the cultures of Aspergillus versicolor, a fungal endophyte of Huperzia serrata, together with 1,7‐dihydroxy‐8‐(methoxycarbonyl)xanthone‐3‐carboxylic acid ( 4 ), β‐diversonolic acid methyl ester ( 5 ), 4‐hydroxyvertixanthone ( 6 ), and sydowinin B ( 7 ). The structures of the new compounds were established by detailed NMR and MS analysis, especially by 2D‐NMR experiments. All xanthones were evaluated for their effects on α‐glucosidase. Compound 4 exhibited a potent inhibitory activity against α‐glucosidase with an IC₅₀ value of 0.24 mM (vs. 0.38 mM for acarbose). The rest of the compounds showed weak or no activity against α‐glucosidase.     

Cyclic RGD Peptides Containing Azabicycloalkane Reverse‐Turn Mimics

The Fmoc‐protected lactams 3 and 4 were used to prepare cyclo(Arg‐Gly‐Asp‐lactam) 1 and cyclo(Arg‐Gly‐Asp‐Phe‐lactam) 2 , which contain the Arg‐Gly‐Asp (RGD) recognition motif. Their solid‐phase synthesis, conformational analysis, and binding to purified α_Vβ₃ and α_Vβ₅ integrins are reported. Compound 1 was found to act as an active and selective inhibitor of the α_Vβ₅ integrin.     

New Sterol Derivatives from the Marine Sponge Xestospongia sp.

Chemical examination of a marine sponge Xestospongia sp. resulted in the isolation of 20 sterol derivatives ( 1 – 20 ), including eight new sterols namely aragusterols J – L ( 1 – 3 ), (5α,7α,12β,22E)‐7,12,18‐trihydroxystigmast‐22‐en‐3‐one ( 4 ), (5α,7α,12β,24R)‐ and (5α,7α,12β,24S)‐7,12,20‐trihydroxystigmastan‐3‐one ( 5 / 6 ), and (5α,7α,12β,22E,24R)‐ and (5α,7α,12β,22E,24S)‐7,12,20‐trihydroxyergost‐22‐en‐3‐one ( 7 / 8 ). The structures of new compounds were determined through extensive spectroscopic analyses and chemical conversion. The sterol diversity was mainly characterized by the presence of a cyclopropane unit at side chain, while compound 4 with 18‐hydroxymethyl group was found in stigmasterol family for the first time. Cytotoxic test revealed the inhibitory effects of compounds 1 , 4 , and 17 against human leukemia cell line K562 with IC₅₀ values of 18.3, 24.1, and 34.3 μm , respectively.     

β-Peptides as Inhibitors of Small-Intestinal Cholesterol and Fat Absorption

Selective lipid transport through the brush-border membrane in the small intestine of mammals is mediated by membrane-bound proteins, the so-called scavenger receptors of class B, type I or II (SR-BI or -BII). These, in turn, are inhibited by certain proteins and synthetic α-peptides that have an amphipathic helix as the binding motif (Fig. 1). In whole cells (test with human colonic carcinoma cells, CaCo-2), on the other hand, the inhibitors are subject to proteolysis. We have now tested six β-peptides (hexa-, hepta-, and nonamers 1 – 6 ), each carrying one to seven water-solubilizing side chains of either Ser or Lys, with a brush-border-membrane (BBM) vesicle model system (rate and IC₅₀ values in Figs. 2 and 3) and with a tightly packed monolayer of CaCo-2 cells (rate in Fig. 4), to find that the rate of transport of cholesterol can be reduced to what may be considered the passive diffusion (`background') level. There is a correlation between the ability of the β-peptides to form an amphipathic-type 3₁₄-helical secondary structure in MeOH and their inhibitory effect (Table 1 and Fig. 5). Although the inhibitory activity of the β-peptides is in only the mM range (Table 2), it is to be compared with no activity at all of previously tested α-peptides and proteins (built of L -amino acids) in CaCo-2 cells. Furthermore, these active β-peptides ( 1 , 5 , and 6 ) contain only seven or nine residues and must be considered simple, first-generation models capable of mimicking the biological activity of amphipathic α-peptide helices in living whole cells.     

Two new ent-atisanes from the root of Euphorbia fischeriana Steud.

Two new ent-atisanes ent-1β,3β,16β,17-tetrahydroxyatisane (1), ent-1β,3α,16β,17-tetrahydroxyatisane (2) together with 11 known diterpenes were isolated from the anti-tumour activity fraction of Euphorbia fischeriana Steud. The compounds were identified by detailed spectroscopic analysis, including extensive 2D-NMR experiments. X-ray analysis was applied to determine the structure of compound 2. All 13 compounds were screened for cytotoxicity in vitro against human tumour MCF-7, HepG-2 and SGC-7901 cell lines. Compounds 1 and 2 showed the inhibitory effects against MCF-7 with IC₅₀ levels of 23.21 and 15.42 μM; simultaneously, compounds 4, 6, 8 and 11 also had definite inhibitory effect against different cell lines.     

Four New Podocarpane‐Type Trinorditerpenes from Aleurites moluccana

Four new podocarpane‐type trinorditerpenenes, (5β,10α)‐12,13‐dihydroxypodocarpa‐8,11,13‐trien‐3‐one ( 1 ), (5β,10α)‐12‐hydroxy‐13‐methoxypodocarpa‐8,11,13‐trien‐3‐one ( 2 ), (5β,10α)‐13‐hydroxy‐12‐methoxypodocarpa‐8,11,13‐trien‐3‐one ( 3 ), and (3α,5β,10α)‐13‐methoxypodocarpa‐8,11,13‐triene‐3,12‐diol ( 4 ), together with four known diterpenes, 12‐hydroxy‐13‐methylpodocarpa‐8,11,13‐trien‐3‐one ( 5 ), spruceanol ( 6 ), ent‐3α‐hydroxypimara‐8(14),15‐dien‐12‐one ( 7 ), and ent‐3β,14α‐hydroxypimara‐7,9(11),15‐triene‐12‐one ( 8 ), were isolated from the twigs and leaves of Aleurites moluccana. Their structures were elucidated by means of comprehensive spectroscopic analyses, including NMR and MS. Except 8 , all compounds were evaluated for their cytotoxicity; compound 4 exhibited moderate inhibitory activity against Raji cells with an IC₅₀ value of 4.24 μg/ml.     

Two new abietane diterpenes huperphlegmarins A and B from Huperzia phlegmaria

Two new abietane diterpenes, huperphlegmarin A–B (1–2), were isolated from the aerial parts of Huperzia phlegmaria (L.) Rothm. (Lycopodiaceae), in addition to five known compounds including lycoxanthol (3), 21β-hydroxyserrat-14-en-3β-yl acetate (4), 21α-hydroxyserrat-14-en-3β-yl acetate (5), 21α-hydroxyserrat-14-en-3β-ol (6), and fawcettidine (7). Their structures were determined by the combination analyses of spectroscopy, including 1D-, 2D-NMR, HRESIMS, CD and comparison with the reported data in the literature. Huperphlegmarin B (2) presented the rare 1,11-epoxy group in the molecule. Compounds 3, 4, 5 and 6 were performed for AChE inhibitory activity and compound 3 showed the inhibitory activity against AChE with IC₅₀ of 465.6 μg/mL.     

Antioxidative sulphated polygalactans from marine macroalgae as angiotensin-I converting enzyme inhibitors

Antioxidant and antihypertensive potential of the sulphated polygalactans isolated from the marine macroalgae Kappaphycus alvarezii and Gracilaria opuntia were assessed by utilising different in vitro systems. The galactans isolated from K. alvarezii possessed significantly greater antioxidative properties as determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH IC₉₀ 0.97 mg/mL) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid (ABTS^.+ IC₉₀ 0.72 mg/mL) scavenging activities than those isolated from G. opuntia (DPPH IC₉₀ 1.2 mg/mL and ABTS 0.86 mg/mL). The sulphated polygalactan →4)-4-O-sulphonato-(2-O-methyl)-β-D-galactopyranosyl-(1→4)-3,6-anhydro-(2-O-methyl)-α-D-galactopyranan from K. alvarezii showed greater angiotensin-I-converting enzyme (ACE) inhibitory activity (IC₅₀ 0.02 μg/mL) than →3)-4-O-sulphonato-(6-O-acetyl)-β-D-galactopyranosyl-(1→4)-3,6-anhydro-(2-O-sulphonato)-α-D-galactopyranosyl-(1→3)-4-O-sulphonato-(6-O-acetyl)-β-D-xylosyl-(1→3)-4-O-sulphonato-(6-O-acetyl)-β-D-galactopyranosyl-(1→4)-3,6-anhydro-(2-O-sulphonato)-α-D-galactopyranan motif extracted from G. opuntia (IC₅₀ 0.70 μg/mL). Structure activity correlation studies displayed that the ACE inhibitory properties of titled polygalactans were directly proportional to their electronic properties and inversely with the steric and hydrophobic characteristics. Putative ACE inhibitory mechanism of action of sulphated galactans from marine macroalgae corroborated the structure bioactivity correlation analysis.     

A novel acylated quercetin glycoside and compounds of inhibitory effects on α-glucosidase from Panax ginseng flower buds

Abstract

A novel acylated quercetin glycoside, floralpanasenoside A (1) and five known flavonoid glycosides, panasenoside (2), quercetin 3-O-(2''-β-D-glucopyranosyl)-β-D- galactopyranoside (3), trifolin (4) kaempferol 7-O-α-L-rhamnoside (5), and afzelin (6) were isolated from the flower buds of Panax ginseng. Their structures were established by spectroscopic data and comparison with the literature values. Four of the six isolated compounds including 1 (IC₅₀ = 62.4) exhibited α-glucosidase inhibitory activity with IC₅₀ values lower than acarbose (385.2?μM). The molecular docking study indicated that 1 bound to the active site of α-glucosidase with numerous hydrogen bond interactions.     

New Triterpenoid Saponins from the Roots of Gypsophila paniculata L.

The seven new triterpenoid saponins 1 – 7 were isolated from the roots of Gypsophila paniculata L. Their structures were established by 1D ‐ and 2D‐NMR techniques, HR‐MS, and acid hydrolysis. The isolated compounds include 3,28‐O‐bidesmosides with or without a 4‐methoxycinnamoyl group (see 1 vs. 2 and 3 ), and 3‐O‐monoglucosides 4 – 7 . All isolated saponins 1 – 7 and their aglycones were evaluated for their α‐glucosidase inhibition activity. Compound 1 showed inhibitory activity against yeast α‐glucosidase with an IC₅₀ value of 100.9±3.3 μM , whereas compounds 2 – 7 were inactive.     

Megastigmane Glycosides from Docynia indica and Their Anti‐inflammatory Activities

Using various chromatographic methods, three new megastigmane glycosides, docynicasides A – C ( 1  –  3 ) and ten known, (6S,9R)‐vomifoliol 9‐O‐β‐d ‐xylopyranosyl‐(1′′→6′)‐O‐β‐d ‐glucopyranoside ( 4 ), hyperin ( 5 ), quercitrin ( 6 ), quercetin 3‐α‐l ‐arabinofuranoside ( 7 ), naringenin 7‐O‐β‐d ‐glucopyranoside ( 8 ), phloridzin ( 9 ), phloretin 2′‐O‐β‐d ‐xylopyranosyl‐(1→6)‐β‐d ‐glucopyranoside ( 10 ), pinosylvin 3‐O‐β‐d ‐glucopyranoside ( 11 ), tormentic acid ( 12 ), and chlorogenic acid methyl ester ( 13 ) were isolated from the fruits of Docynia indica. Their chemical structures were elucidated by physical and chemical methods. All the isolated compounds were evaluated for the inhibitory activity on NO production in LPS‐stimulated BV2 cells. As the results, compounds 3  –  5 showed significant inhibitory activity on LPS‐stimulated NO production in BV2 cells with the IC₅₀ values ranging from 21.0 to 29.3 μm .