Castanospermine Analogues Research Articles

Sp2‐Iminosugar α‐glucosidase inhibitor 1‐C‐octyl‐2‐oxa‐3‐oxocastanospermine specifically affected breast cancer cell migration through Stim1, β1‐integrin, and FAK signaling pathways

Aberrant glycosylation changes on many glycoproteins are often related to cancer progression and metastasis. sp2 -Iminosugar-type castanospermine analogues, inhibitors of α-glucosidases, have been reported to exhibit antitumor activity. However, their effects on cell migration and the underlying molecular mechanism are not fully understood. Here, we investigated the effect of the pseudo-C-octyl glycoside 2-oxa-3-oxocastanospermine derivatives (CO-OCS) on breast cancer cells (MCF-7 and MDA-MB-231 cells), and MCF-10A mammary normal cell lines. We showed that CO-OCS treatment results in the drastic decrease of breast cancer cell migration without affecting cell proliferation. Furthermore, CO-OCS significantly reduced both the expression of β1-integrin, which is a crucial interacting partner of Focal Adhesion Kinase (FAK), and the phosphorylation rates of FAK and ERK1/2. CO-OCS also drastically reduced Ca2+ entry through Store Operated Channels (SOC). Orai1 and Stim1, two N-glycosylated proteins, are involved in Store-Operated Calcium Entry (SOCE), and are essential for breast tumor cell migration. Our results showed that CO-OCS decreased the expression, at the protein level, of Stim1 without affecting that of Orai1. Moreover, cell migration and SOCE were attenuated by CO-OCS as well as when Stim1 was silenced. In contrast, in MCF-10A cells, CO-OCS slightly reduced cell migration, but was without effect on gene expression of Stim1, Orai1, β1-integrin, or FAK and ERK1/2 activation. Our results provide strong evidence for a significant effect of CO-OCS on breast cancer cell migration and support that this effect was associated with β1-integrin, Stim1, and FAK signaling pathways.

Contribution to the synthesis of polyhydroxylated indolizidines starting from sugar isothiocyanates

A straightforward stereoselective route towards castanospermine analogues starting from the corresponding d-gluco- and l-ido-hexofuranose isothiocyanates (5S)-2 and (5R)-2 is described. The key transformations of this approach rely on ring-closing metathesis and reductive amination to form the final polyhydroxylated indolizidines 10–13 in good overall yields.

Synthesis of multibranched australine derivatives from reducing castanospermine analogues through the Amadori rearrangement of gem-diamine intermediates: selective inhibitors of β-glucosidase.

A practical one-pot synthesis of bi- and triantennated australine analogues from a pivotal sp(2)-iminosugar-type reducing castanospermine precursor is reported. The transformation involves a gem-diamine intermediate that undergoes the indolizidine → pyrrolizidine Amadori-type rearrangement and proceeds under strict control of the generalized anomeric effect to afford a single diastereomer. The final compounds behave as selective competitive inhibitors of β-glucosidase and are promising candidates as pharmacological chaperones for Gaucher disease.

ChemInform Abstract: N‐Thiocarbonyl Iminosugars: Synthesis and Evaluation of Castanospermine Analogues Bearing Oxazole‐2(3H)‐thione Moieties.

A straightforward and efficient synthetic route to a new class of glycosidase inhibitors containing an oxazole-2(3H)-thione moiety has been devised. The approach involves the formation of α-hydroxy ketones, which, after condensation with thiocyanic acid, leads to the formation of the heterocycle. By exploiting the ability of the nitrogen atom of oxazoline-2thione precursors to act as nucleophiles in intramolecular addition, castanospermine analogues could be readily prepared in good overall yields. Glycosidase inhibitory activity com

N‐Thiocarbonyl Iminosugars: Synthesis and Evaluation of Castanospermine Analogues Bearing Oxazole‐2(3H)‐thione Moieties

AbstractA straightforward and efficient synthetic route to a new class of glycosidase inhibitors containing an oxazole‐2(3H)‐thione moiety has been devised. The approach involves the formation of α‐hydroxy ketones, which, after condensation with thiocyanic acid, leads to the formation of the heterocycle. By exploiting the ability of the nitrogen atom of oxazoline‐2‐thione precursors to act as nucleophiles in intramolecular addition, castanospermine analogues could be readily prepared in good overall yields. Glycosidase inhibitory activity compared to oxazolidinethione analogues showed a strong influence of the double bond, for example with pseudoiminosugar 19, by suppressing α‐glucosidase inhibition and introducing, to a moderate level, β‐glucosidase inhibitory activity. Reactivities showed the propensity of oxazole‐2(3H)‐thiones – especially when fused on carbohydrate frames – to convert into 1,3‐oxazolidine‐2‐thione aminals through nucleophilic addition to the double bond, leading to unexpected tricyclic structure 21.

New Castanospermine Glycoside Analogues Inhibit Breast Cancer Cell Proliferation and Induce Apoptosis without Affecting Normal Cells

sp2-Iminosugar-type castanospermine analogues have been shown to exhibit anti-tumor activity. However, their effects on cell proliferation and apoptosis and the molecular mechanism at play are not fully understood. Here, we investigated the effect of two representatives, namely the pseudo-S- and C-octyl glycoside 2-oxa-3-oxocastanospermine derivatives SO-OCS and CO-OCS, on MCF-7 and MDA-MB-231 breast cancer and MCF-10A mammary normal cell lines. We found that SO-OCS and CO-OCS inhibited breast cancer cell viability in a concentration- and time-dependent manner. This effect is specific to breast cancer cells as both molecules had no impact on normal MCF-10A cell proliferation. Both drugs induced a cell cycle arrest. CO-OCS arrested cell cycle at G1 and G2/M in MCF-7 and MDA-MB-231cells respectively. In MCF-7 cells, the G1 arrest is associated with a reduction of CDK4 (cyclin-dependent kinase 4), cyclin D1 and cyclin E expression, pRb phosphorylation, and an overexpression of p21Waf1/Cip1. In MDA-MB-231 cells, CO-OCS reduced CDK1 but not cyclin B1 expression. SO-OCS accumulated cells in G2/M in both cell lines and this blockade was accompanied by a decrease of CDK1, but not cyclin B1 expression. Furthermore, both drugs induced apoptosis as demonstrated by the increased percentage of annexin V positive cells and Bax/Bcl-2 ratio. Interestingly, in normal MCF-10A cells the two drugs failed to modify cell proliferation, cell cycle progression, cyclins, or CDKs expression. These results demonstrate that the effect of CO-OCS and SO-OCS is triggered by both cell cycle arrest and apoptosis, suggesting that these castanospermine analogues may constitute potential anti-cancer agents against breast cancer.

Synthesis of C1- and C8a-epimers of (+)-castanospermine from d-glucose derived γ,δ-epoxyazide: intramolecular 5- endo epoxide opening approach

A concise synthesis of two diastereomers of (+)-castanospermine namely 1- and 8a- epi-castanospermine 1b and 1c, respectively, is reported from d-glucose. The methodology involves stereoselective cross metathesis of d-glucose derived alkene 2 with 4-bromo-1-butene followed by azide displacement and m-CPBA oxidation to afford diastereomeric γ,δ-epoxyazides 5a/ 5b. The Staudinger reaction of epoxyazide 5a followed by reaction with benzylchloroformate (CbzCl) unexpectedly furnished 1,3-oxazinan-2-one derivative 7 whose stereochemistry was establish by single crystal X-ray. This helps to assign the stereochemistry in the epoxidation reaction. The reduction of 5a/ 5b was then carried out by transfer hydrogenation to provide γ,δ-epoxyamine that concomitantly undergoes intramolecular 5- endo-tet cyclization to afford hydroxypyrrolidine ring skeleton with sugar framework-a precursor to castanospermine analogues 1b/ 1c.

ChemInform Abstract: Synthesis of N‐, S‐, and C‐Glycoside Castanospermine Analogues with Selective Neutral α‐Glucosidase Inhibitory Activity as Antitumor Agents.

AbstractThree novel castanospermine analogues (III), (VIII), and (XIII) are synthesized and found to display selective inhibitory activity against neutral α‐glucosidase as well as promising anticancer activity against human breast carcinoma cell lines.

Synthesis of N-, S-, and C-glycoside castanospermine analogues with selective neutral α-glucosidase inhibitory activity as antitumour agents

sp(2)-Iminosugar-type castanospermine analogues bearing an alpha-configured N-, S-, or C-linked pseudoanomeric group have been designed as selective inhibitors of the neutral alpha-glucosidases involved in N-glycoprotein processing; evaluation in breast cancer cell growth indicated a significant antiproliferative potential that was dependent on the nature of the pseudoanomeric group.

A new synthetic access to bicyclic polyhydroxylated alkaloid analogues from pyranosides

A facile, versatile and stereoselective synthesis of bicyclic polyhydroxylated alkaloids as castanospermine analogues is described. The synthetic route started from methyl pyranosides. The key steps involved a high-yielding expeditious one-pot tandem reaction from alkenes to N-substituted delta-lactams. The delta-lactams were stereoselectively vinylated to give the dienes, which were followed by the ring-closing metathesis to produce the cyclized products. The functional group transformations of the resulting bicyclic compounds furnished diverse polyhydroxylated alkaloids in good yields.

Glycosidase inhibition by ring-modified castanospermine analogues: tackling enzyme selectivity by inhibitor tailoring

Synthesis of a panel of iso(thio)urea-type ring-modified castanospermine analogues bearing a freely mutarotating pseudoanomeric hydroxyl group results in tight-binding beta-glucosidase inhibitors with unusual binding signatures; the presence of an N-octyl substituent imparts a remarkable anomeric selectivity, promoting strong binding of the appropriate beta-anomer by the beta-glucosidase.

Efficient synthesis of 2,6,7,8-tetrahydroxyindolizidines (castanospermine analogues) via the dipolar cycloadditions of N-benzyl- C-(tetrofuranos-4-yl)nitrones to methyl acrylate

The dipolar cycloaddition of ( Z)- N-benzyl-(3- O-benzyl-1,2- O-isopropylidene-α- d-ribofuranos-5-ylidene)amine N-oxide to methyl acrylate gives a 53:16:26:5 diastereomeric mixture of isoxazolidine derivatives. The dipolar cycloaddition of the xylo analogue to methyl acrylate is more diastereoselective, producing a 44:13:43 mixture of only three diastereomers. The ribo-configured adducts have been converted (4 steps only) into the new (2 R,6 S,7 S,8 R,8a R)-, (2 S,6 S,7 S,8 R,8a R)-, (2 S,6 S,7 S,8 R,8a S)- and (2 R,6 S,7 S,8 R,8a S)-2,6,7,8-tetrahydroxyindolizidines. Similarly, the two xylo-configured major isoxazolidine derivatives were converted into the known derivatives (2 R,6 S,7 R,8 R,8a S)- and (2 S,6 S,7 R,8 R,8a R)-2,6,7,8-tetrahydroxyindolizidines. The six isomeric indolizidine derivatives obtained have been evaluated for their inhibiting activities towards 15 glycosidases. Only the (2 R,6 S,7 S,8 R,8a R)-configured isomer is a selective inhibitor of amyloglucosidases from Aspergillus niger (IC 50 = 350 μM) and from Rhizopus mold (IC 50 = 90 μM, K i = 195 μM, non-competitive), the other indolizidines show very little inhibitory activity at 1 mM concentration.

Generalized anomeric effect in action: synthesis and evaluation of stable reducing indolizidine glycomimetics as glycosidase inhibitors.

A series of aminoketalic castanospermine analogues incorporating a stereoelectronically anchored axial hydroxy group at the pseudoanomeric stereocenter (C-5) have been synthesized to satisfy the need for glucosidase inhibitors that are highly selective for alpha-glucosidases. The polyhydroxylated bicyclic system was built from readily available hexofuranose derivatives through a synthetic scheme that involved (i) the construction of a five-membered cyclic (thio)carbamate or (thio)urea moiety at the nonreducing end and (ii) the intramolecular nucleophilic addition of the heterocyclic thiocarbamic nitrogen atom to the masked aldehyde group of the monosaccharide. A biological screening of the resulting reducing 2-oxa- and 2-azaindolizidines against several glycosidase enzymes is reported.

Inhibition of Glycoprotein Processing and HIV Replication by Castanospermine Analogues

Inhibitors of glycoprotein processing enzymes have been shown to have activity against HIV. Several analogues of the known glucosidase I inhibitor, castanospermine (CAST), were synthesized and evaluated for their inhibitory effect on glucosidases and for antiviral activity against Moloney murine leukemia virus (MOLV) and HIV-1. The most effective analogue was 6-O-butanoyl CAST (B-CAST, MDL 28,574) with an IC50 of 0.05 micrograms/mL against MOLV. A correlation between inhibition of glucosidase I and MOLV replication was observed. This analogue was further evaluated against HIV-induced syncytial formation in HeLa T4+ cells and against productive infection in JM cells infected with HIV 1 (GB8 strain). B-CAST showed an IC50 of 0.3 micrograms/mL in the HeLa T4+ assay, compared to CAST at 11 micrograms/mL. The compound also was more potent (IC50:0.15 micrograms/mL) than CAST (4-6 micrograms/mL) in JM cells. The antiretroviral activity of B-CAST was further confirmed in Friend leukemia virus (FLV) infection in mice. B-CAST showed equivalent activity to AZT and was more potent than CAST in inhibiting FLV-induced splenomegaly in mice. The data presented herein suggest the potential of these novel glucosidase inhibitors as anti-HIV agents.

The structural basis of the inhibition of human glycosidases by castanospermine analogues

A series of epimers and deoxy derivatives of castanospermine has been synthesized to investigate the contribution of the different chiral centres to the specificity and potency of inhibition of human liver glycosidases. Castanospermine inhibits all forms of alpha- and beta-D-glucosidases, but alteration to any of the five chiral centres in castanospermine markedly decreases the inhibition. 6-Epicastanospermine, which is related to D-pyranomannose in the same way as castanospermine is to D-pyranoglucose, does not inhibit lysosomal (acidic) alpha-mannosidase, but is a good inhibitor of the cytosolic or neutral alpha-mannosidase. Conversely, 1-deoxy-6-epicastanospermine inhibits acidic alpha-mannosidase strongly, but not the neutral alpha-mannosidase. An explanation of this different inhibition based on preferential recognition of different configurations of mannose by the different forms of alpha-mannosidase is postulated. All derivatives of 6-epicastanospermine also have the minimum structural feature for the inhibition of alpha-L-fucosidase, but those with a beta-anomeric substituent do not inhibit the enzyme, or do so very weakly. 1-Deoxy-6,8a-diepicastanospermine, which has four chiral centres identical with alpha-L-fucose, is, however, a potent inhibitor of alpha-L-fucosidase (Ki 1.3 microM).

A new approach to swainsonine and castanospermine analogues

(1S, 2R, 7R, 7aR)- 1,2,7-Trihydroxypyrrolizidine ( 1) is prepared by elaboration of an erythrose derivative ( 4) via an asymmetric allylation reaction; this approach promises to be widely applicable to syntheses of polyhydroxylated indolizidine and pyrrolizidine alkaloids.