Chemical modification of aminocyclitol antibiotics

The aminocyclitol antibiotic neamine has been chemically modified at the hydroxyl group on C-6 of the 2-deoxystreptamine moiety. The partially acetylated neamine derivatives, 6,3′,4′-tri-O-acetyl- (3) and 5,3′,4′-tri-O-acetyl-1,3,2′,6′-tetra-N-(ethoxycarbonyl)neamine (4), were prepared by random hydrolysis of the 5,6-O-ethoxyethylidene derivative (2), followed by chromatographic purification. Condensation of 4 and 2,3,5-tri-O-benzoyl-d-ribofuranosyl chloride led to 6-O-(β-d-ribofuranosyl)neamine (7). Analogous condensation of 4 with 2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl bromide or 2,3,4,6-tetra-O-acetyl-α-d-galactopyranosyl bromide afforded the corresponding 6-O-(d-hexopyranosyl)neamines.     

Design,synthesis, and biological evaluation of novel water-soluble triptolide derivatives: Antineoplastic activity against imatinib-resistant CML cells bearing T315I mutant Bcr-Abl

Imatinib (STI571) is the frontline targeted-therapeutic agent for patients with chronic myelogenous leukemia (CML). However, resistance to imatinib due to point mutations in Bcr-Abl kinase domain is an emerging problem. We recently reported that triptolide (compound 1) could effectively kill CML cells including those harboring T315I mutant Bcr-Abl. In the present study, we designed a series of C-14 triptolide derivatives with C-14-hydroxyl substituted by different amine esters (3–18): 3–6 and 13 (by aliphatic chain amine esters); 7–9, 11, 12 and 15–18 (by alicyclic amine esters with different size), and 10 and 14 (by aralkylamine esters).The compounds were examined for their antineoplastic activity against CML cells (including KBM5-T315I cells) in terms of proliferation inhibition, apoptosis and signal transduction. Nude mouse xenograft model was also used to evaluate the in vivo activity. Compounds 2–9, 11–14, 17 and 18 exhibited a potent inhibitory activity against KBM5 and KBM5-T315I cells. This series of derivatives down-regulated Bcr-Abl mRNA. Compounds 4, 5, 8 and 9 were further examined for their impact on signaling and apoptosis with immunoblotting. Compound 5 was chosen for evaluation in a nude mouse xenograft model. The stereo-hindrance of C-14 group appeared to be responsible for the antitumor effect. The computational small molecule-protein docking analysis illustrated the possible interaction between compound 9 and RNA polymerase II. Our results suggest that this series of derivatives may be promising agents to overcome imatinib-resistance caused by the Bcr-Abl-T315I mutation.     

Synthesis and antibacterial activity of a series of novel 9-O-acetyl- 4′-substituted 16-membered macrolides derived from josamycin

A series of novel 9-O-acetyl-4′-substituted 16-membered macrolides derived from josamycin has been designed and synthesized by cleavage of the mycarose of josamycin and subsequent modification of the 4′-hydroxyl group. These derivatives were evaluated for their in vitro antibacterial activities against a panel of Staphylococcus aureus and Staphylococcus epidermidis. 15 (4′-O-(3-Phenylpropanoyl)-9-O-acetyl-desmycarosyl josamycin) and 16 (4′-O-butanoyl-9-O-acetyl-desmycarosyl josamycin) exhibited comparable activities to josamycin against S. aureus (MSSA) and S. epidermidis (MSSE).     

Vancomycin analogs: Seeking improved binding of d-Ala-d-Ala and d-Ala-d-Lac peptides by side-chain and backbone modifications

In order to seek vancomycin analogs with improved performance against VanA and VanB resistant bacterial strains, extensive computational investigations have been performed to examine the effects of side-chain and backbone modifications. Changes in binding affinities for tripeptide cell-wall precursor mimics, Ac₂-l-Lys-d-Ala-d-Ala (3) and Ac₂-l-Lys-d-Ala-d-Lac (4), with vancomycin analogs were computed with Monte Carlo/free energy perturbation (MC/FEP) calculations. Replacements of the 3-hydroxyl group in residue 7 with small alkyl or alkoxy groups, which improve contacts with the methyl side chain of the ligands’ d-Ala residue, are predicted to be the most promising to enhance binding for both ligands. The previously reported amine backbone modification as in 5 is shown to complement the hydrophobic modifications for binding monoacetylated tripeptides. In addition, replacement of the hydroxyl groups in residues 5 and 7 by fluorine is computed to have negligible impact on binding the tripeptides, though it may be pharmacologically advantageous.     

Studies on the synthesis of neamine-dinucleosides and neamine-PNA conjugates and their interaction with RNA

Two types of neamine derivatives, neamine-dinucleotide conjugates 8a-g and neamine-PNA conjugates 12a-c and 14a-d, were synthesized. Compound 8a-g were synthesized by the condensation of azido-neamine with dinucleotide-5'-carboxylic acids, followed by reduction and deprotection. Compound 12a-c and 14a-d were synthesized by the similar strategy. The binding affinities of conjugates 8a-g, 12a-c, and 14a-d towards 16S RNA, 18S RNA, and TAR RNA were evaluated by SPR. It indicates that conjugates 12a-c and 14a-d interact with 16S, 18S RNA at the same level as that of neamine, 14a and 14d show about twofold binding affinities to TAR RNA compared to that of neamine. However, the neamine-dinucleotide conjugates 8a-g exhibit very weak binding affinities to 16S, 18S, and TAR RNA, computer modelling results that negative-negative electrostatic repulsion of phosphate group in compound 8a-g and RNA leads to a sharp decrease of the binding affinities compared with that of neamine, neamine-nucleoside and neamine-PNA conjugates.     

Synthesis and structure–activity relationship of 2-phenyliminochromene derivatives as inhibitors for aldo–keto reductase (AKR) 1B10

Inhibitors of a human member (AKR1B10) of the aldo–keto reductase superfamily are regarded as promising therapeutics for the treatment of cancer. Recently, we have discovered (Z)-2-(4-methoxyphenylimino)-7-hydroxy-N-(pyridin-2-yl)-2H-chromene-3-carboxamide (1) as the potent competitive inhibitor using the virtual screening approach, and proposed its 4-methoxy group on the 2-phenylimino moiety as an essential structural prerequisite for the inhibition. In this study, 18 derivatives of 1 were synthesized and their inhibitory potency against AKR1B10 evaluated. Among them, 7-hydroxy-2-(4-methoxyphenylimino)-2H-chromene-3-carboxylic acid benzylamide (5n) was the most potent inhibitor showing a K_i value of 1.3 nM. The structure–activity relationship of the derivatives indicated that the 7-hydroxyl group on the chromene ring, but not the 4-methoxy group, was absolutely required for inhibitory activity, The molecular docking of 5n in AKR1B10 and site-directed mutagenesis of the enzyme residues suggested that the hydrogen-bond interactions between the 7-hydroxyl group of 5n and the catalytic residues (Tyr49 and His111) of the enzyme, together with a π-stacking interaction of the benzylamide moiety of 5n with Trp220, are important for the potent inhibition.     

Structure–anti-MRSA activity relationship of macrocyclic bis(bibenzyl) derivatives

We synthesized a series of macrocyclic bis(bibenzyl) derivatives, including riccardin-, isoplagiochin- and marchantin-class structures, and evaluated their antibacterial activity towards methicillin-resistant Staphylococcus aureus (anti-MRSA activity). The structure–activity relationships and the results of molecular dynamics simulations indicated that bis(bibenzyl)s with potent anti-MRSA activity commonly have a 4-hydroxyl group at the D-benzene ring and a 2-hydroxyl group at the C-benzene ring in the hydrophilic part of the molecule, and an unsubstituted phenoxyphenyl group in the hydrophobic part of the molecule containing the A–B-benzene rings. Pharmacological characterization of the bis(bibenzyl) derivatives and 2-phenoxyphenol fragment 25, previously proposed as the minimum structure of riccardin C 1 for anti-MRSA activity, indicated that they have different action mechanisms: the bis(bibenzyl)s are bactericidal, while 25 is bacteriostatic, showing only weak bactericidal activity.     

Binding of influenza virus hemagglutinin to analogs of its cell-surface receptor, sialic acid: analysis by proton nuclear magnetic resonance spectroscopy and X-ray crystallography.

The interaction between influenza virus hemagglutinin and its cell-surface receptor, 5-N-acetylneuraminic acid (sialic acid), was probed by the synthesis of 12 sialic acid analogs, including derivatives at the 2-carboxylate, 5-acetamido, 4-, 7-, and 9-hydroxyl, and glycosidic positions. The equilibrium dissociation constants of these analogs were determined by nuclear magnetic resonance spectroscopy. Ligand modifications that reduced or abolished binding included the replacement of the 2-carboxylate with a carboxamide, the substitution of azido or N-benzyloxycarbonyl groups for the 5-acetamido group, and the replacement of the 9-hydroxyl with amino or O-acetyl moieties. Modifications having little effect on binding included the introduction of longer chains at the 4-hydroxyl position, the replacement of the acetamido methyl group with an ethyl group, and the removal of the 7-hydroxyl group. X-ray diffraction studies yielded 3 A resolution crystal structures of hemagglutinin in complex with four of the synthetic analogs [alpha-2-O-methyl-, 4-O-acetyl-alpha-2-O-methyl-, 9-amino-9-deoxy-alpha-2-O-methyl-, and alpha-2-O-(4'-benzylamidocarboxybutyl)-N-acetylneuraminic acid] and with the naturally occurring cell-surface saccharide (alpha 2-3)sialyllactose. The X-ray studies unambiguously establish the position and orientation of bound sialic acid, indicate the position of the lactose group of (alpha 2-3)sialyllactose, and suggest the location of an alpha-glycosidic chain (4'-benzylamidocarboxybutyl) that increases the binding affinity of sialic acid by a factor of about 3. Although the protein complexed with alpha-2-O-methylsialic acid contains the mutation Gly-135-->Arg near the ligand binding site, the mutation apparently does not affect the ligand's position. The X-ray studies allow us to interpret the binding affinities in terms of the crystallographic structure. The results suggest further experiments which could lead to the design of tight binding inhibitors of possible therapeutic value.     

Two-dimensional combinatorial screening and the RNA Privileged Space Predictor program efficiently identify aminoglycoside–RNA hairpin loop interactions

Herein, we report the identification of RNA hairpin loops that bind derivatives of kanamycin A, tobramycin, neamine, and neomycin B via two-dimensional combinatorial screening, a method that screens chemical and RNA spaces simultaneously. An arrayed aminoglycoside library was probed for binding to a 6-nucleotide RNA hairpin loop library (4096 members). Members of the loop library that bound each aminoglycoside were excised from the array, amplified and sequenced. Sequences were analyzed with our newly developed RNA Privileged Space Predictor (RNA-PSP) program, which analyzes selected sequences to identify statistically significant trends. RNA-PSP identified the following unique trends: 5′UNNNC3′ loops for the kanamycin A derivative (where N is any nucleotide); 5′UNNC3′ loops for the tobramycin derivative; 5′UNC3′ loops for the neamine derivative; and 5′UNNG3′ loops for the neomycin B derivative. The affinities and selectivities of a subset of the ligand–hairpin loop interactions were determined. The selected interactions have K_d values ranging from 10 nM to 605 nM. Selectivities ranged from 0.4 to >200-fold. Interestingly, the results from RNA-PSP are able to qualitatively predict specificity based on overlap between the RNA sequences selected for the ligands. These studies expand the information available on small molecule–RNA motif interactions, which could be useful to design ligands targeting RNA.     

Substituted phenyl[(5-benzyl-1,3,4-oxadiazol-2-yl)sulfanyl]acetates/acetamides as alkaline phosphatase inhibitors: Synthesis,computational studies,enzyme inhibitory kinetics and DNA binding studies

Substituted phenyl[(5-benzyl-1,3,4-oxadiazol-2-yl)sulfanyl]acetates/acetamides 9a-j were synthesized as alkaline phosphatase inhibitors. Phenyl acetic acid 1 through a series of reactions was converted into 5-benzyl-1,3,4-oxadiazole-2-thione 4. The intermediate oxadiazole 4 was then reacted with chloroacetyl derivatives of phenols 6a-f and anilines derivatives 8a-d to afford the title oxadiazole derivatives 9a-j. All of the title compounds 9a-j were evaluated for their inhibitory activity against human alkaline phosphatise (ALP). It was found that compounds 9a-j exhibited good to excellent alkaline phosphatase inhibitory activity especially 9h displayed potent activity with IC₅₀ value 0.420 ± 0.012 µM while IC₅₀ value of standard (KH₂PO₄) was 2.80 µM. The enzyme inhibitory kinetics of most potent inhibitor 9h was determined by Line-weaever Burk plots showing non-competitive mode of binding with enzyme. Molecular docking studies were performed against alkaline phosphatase enzyme (1EW2) to check the binding affinity of the synthesized compounds 9a-j against target protein. The compound 9h exhibited excellent binding affinity having binding energy value (−7.90 kcal/mol) compared to other derivatives. The brine shrimp viability assay results proved that derivative 9h was non-toxic at concentration used for enzyme assay. The lead compound 9h showed LD₅₀ 106.71 µM while the standard potassium dichromate showed LD₅₀ 0.891 µM. The DNA binding interactions of the synthesized compound 9h was also determined experimentally by spectrophotometric and electrochemical methods. The compound 9h was found to bind with grooves of DNA as depicted by both UV–Vis spectroscopy and cyclic voltammetry with binding constant values 7.83 × 10³ and 7.95 × 10³ M⁻¹ respectively revealing significant strength of 9h-DNA complex. As dry lab and wet lab results concise each other it was concluded that synthesized compounds, especially compound 9h may serve as lead compound to design most potent inhibitors of human ALP.     

Novel biotransformation processes of dihydroartemisinic acid and artemisinic acid to their hydroxylated derivatives by two plant cell culture systems

Novel biotransformation processes of dihydroartemisinic acid (1) and artemisinic acid (2) to their hydroxylated derivatives were investigated using the cell suspension cultures of Catharanthus roseus and Panax quinquefolium crown galls as two biocatalyst systems. Five biotransformation products, 3-α-hydroxydihydroartemisinic acid (3), 3-β-hydroxydihydroartemisinic acid (4), 15-hydroxy-cadin-4-en-12-oic acid (5), 3-α-hydroxyartemisinic acid (6) and 3-β-hydroxyartemisinic acid (7), were isolated by chromatograph methods and identified by the analysis of ¹H NMR, ¹³C NMR, and ESI-MS spectra. Compounds 3–5 were obtained for the first time by biotransformation process. It was also the first time to transform artemisinic acid to yield epimeric 3-hydroxy artemisinic acids in plant cell culture system. The biocatalyst system of C. roseus cell cultures showed a great capacity of regio- and stereo-selective hydroxylation in allyl group of the exogenous substrates. The results also showed that the biocatalyst system of P. quinquefolium crown galls possessed the ability to hydroxylate propenyl group of exogenous substrates in a regio- and substrate-selective manner. Furthermore, the in vitro antitumor activity of the hydroxyl products was evaluated by MTT assay. The result indicated that α-hydroxyl products possessed stronger antitumor activity than β-hydroxyl products against the HepG2 and GLC-82 cell lines.     

Selective cyclooxygenase inhibition and ulcerogenic liability of some newly prepared anti-inflammatory agents having thiazolo[4,5-d]pyrimidine scaffold

Novel candidates of thiazolo[4,5-d]pyrimidines (9a-l) were synthesized and their structures were elucidated by spectral and elemental analyses. All the novel derivatives were screened for their cyclooxygenase inhibitory effect, anti-inflammatory activity and ulcerogenic liability. All the new compounds exhibited anti-inflammatory activity, especially 1-(4-[7-(4-nitrophenyl)-5-thioxo-5,6-dihydro-3H-thiazolo[4,5-d]pyrimidin-2-ylideneamino]phenyl)ethanone (9g) was the most active derivative with 57%, 88% and 88% inhibition of inflammation after 1, 3 and 5h, respectively. Furthermore, this derivative 9g recorded higher anti-inflammatory activity than celecoxib which showed 43%, 43% and 54% inhibition after 1, 3 and 5h, sequentially. Moreover, the target derivatives 9a-l demonstrated moderate to high potent inhibitory action towards COX-2 (IC₅₀ = 0.87–3.78 µM), in particular, the derivatives 9e (IC₅₀ = 0.92 µM), 9g (IC₅₀ = 0.87 µM) and 9k (IC₅₀ = 1.02 µM) recorded higher COX-2 inhibitory effect than the selective COX-2 inhibitor drug celecoxib (IC₅₀ = 1.11 µM). The in vivo potent compounds (9e, 9g and 9k) caused variable ulceration effect (ulcer index = 5–12.25) in comparison to that of celecoxib (ulcer index = 3). Molecular docking was performed to the most potent COX-2 inhibitors (9e, 9g and 9k) to explore the binding mode of these derivatives with Cyclooxygenase-2 enzyme.     

Synthesis and in vitro cytotoxicity of andrographolide-19-oic acid analogues as anti-cancer agents

The synthesis of a series of andrographolide-19-oic acid derivatives was described and their in vitro anti-tumor activity against two human cell lines was evaluated. Most compounds were found to exhibit significant cytotoxicity, better than andrographolide, and compounds 9d and 9b were identified as the most potent with IC₅₀ values of 1.18 and 6.28 μm against HCT-116 and MCF-7 cell lines, respectively. The preliminary results indicated that the oxidation of C-19-hydroxyl group of andrographolide to corresponding carboxyl group and the subsequent esterification of the formed carboxylic acid led to considerable improvement in cytotoxicity against the cancer cells.     

Synthesis and cytotoxicity against KB and NCI-H187 cell lines of sporogen AO-1 analogues

20 Analogues of sporogen AO-1 were synthesized by chemical modification at α,β-unsaturated carbonyl, 3-hydroxyl and vinylic methyl groups of sporogen AO-1 precursor, and were evaluated for their cytotoxic activities against human oral epidermoid carcinoma (KB) and human small cell lung (NCI-H187) cancer cell lines. Structure-activity relationship study indicated the importance of α,β-unsaturated carbonyl moiety for both cancer cell lines. Vinylic methyl and R-configuration of 3-hydroxyl group were crucial for cytotoxicity toward KB cells. In contrast, conversion of vinylic methyl and 3-hydroxyl groups to ketone moieties afforded triketone 19 which displayed comparable cytotoxicity against NCI-H187 cells lines to sporogen AO-1, and was more potent than ellipticine, a standard drug. Interestingly, compound 19 was weakly cytotoxic toward Vero cells, whereas sporogen AO-1 showed strong cytotoxicity.     

Apoptotic induction mediated p53 mechanism and Caspase-3 activity by novel promising cyanoacrylamide derivatives in breast carcinoma

New cyanoacrylamide derivatives were theoretically examined for their binding abilities to a protein model of apoptosis inhibitor proteins x-IAP and c-IAP1 using molecular modeling. The two compounds 5a and 5b proved promising IAP antagonists, where they have good binding affinity toward the selected active domains. Anticancer activity of all derivatives was performed on different human cancer cell lines (HCT116, Caco₂, and MCF7) as well as normal line (HBF4). Data revealed that breast carcinoma was more sensitive to the novel compounds than other lines especially compounds 5a and 5b, but all derivatives lost their cytotoxic effect in case of Caco2 cell line and they showed low cytotoxic effect toward HCT116 cells except compound 3. The flow cytometric analysis revealed that the two compounds 5a and 5b induced apoptosis to 46.5% and 54.8% respectively, relative to control 8.06%. In addition, PCR results indicated that the two compounds 5a and 5b induced the expression of p53 gene and decreased induction of BCL2 (anti-apoptotic gene), while the two compounds have no effect on the protein expression of Caspase-9. By monitoring the presence of Caspase-3 which was a mean to detect apoptotic death in breast carcinoma, the two compounds have stimulated the induction of apoptosis by increasing the production of Caspase-3 protein. Finally, it was concluded that the two compounds 5b and 5a have the most promising anti-cancer activity against human breast carcinoma (MCF7), and it is believed that the anticancer activities of these two compounds were due to being the most effective in the inhibition of a member of IAPs groups, leading to activation of p53 gene and the Caspase-3 dependent apoptosis.     

Synthesis and evaluation of 9-O-substituted berberine derivatives containing aza-aromatic terminal group as highly selective telomeric G-quadruplex stabilizing ligands

A series of new 9-O-substituted berberine derivatives (4a–j) as telomeric quadruplex ligands was synthesized and evaluated. The results from biophysical and biochemical assay indicated that introducing of positive charged aza-aromatic terminal group into the side chain of 9-position of berberine significantly improved the binding ability with G-quadruplex, and exhibited the inhibitory effect on the hybridization and on telomerase activity. These derivatives showed excellent selectivity for telomeric G-quadruplex DNA over duplex.     

A refined model of the sugar binding site of yeast hexokinase B.

The sugar binding site of monomeric yeast hexokinase B complexed with the competitive inhibitor o-toluoylglucosamine has been examined in the model resulting from a crystallographic refinement at 2·1 Å resolution. Difference Fourier maps calculated assuming various sugar configurations demonstrate that the o-toluoylglucosamine binds in the chair equatorial conformation with its 1-hydroxyl axial (α-anomer). The absence of a chemically derived amino acid sequence has complicated our interpretations of sugar-enzyme interactions. Nevertheless, we conclude that the carboxyl group of Asp189 is hydrogen-bonded to both the 6- and 4-hydroxyl groups. The 4-hydroxyl group is hydrogen-bonded also to Asx188 and Asx215, while the 3-hydroxyl is interacting with both Asx245 and Asx 188, consistent with the enzyme's observed sugar specificity. The carboxyl group of Asp 189 is excluded from solvent in the presence of glucose and may be acting as a general base to enhance the nucleophilicity of the 6-hydroxyl group and thereby promote its attack on the γ-phosphate of ATP.Glucose is shown to bind to the enzyme in the same orientation and conformation as the sugar moiety of o-toluoylglucosamine, so that the 6-hydroxyl group and the carboxyl of Asp 189 are in identical positions in complexes with these two sugars. The fact that o-toluoylglucosamine is not a substrate must be explained by two observations. First, the binding of glucose results in one lobe rotating by 12 ° relative to the other lobe, thereby closing off the slit into which the sugar has bound (Bennett &; Steitz, unpublished results). Second, o-toluoylglucosamine does not produce this conformational change, because the bulky toluoyl group prevents the closing of this slit between the two lobes. We conclude, therefore, that the large glucose-induced conformational change must be essential for subsequent catalytic steps.It appears unlikely from this study that thiols play any direct role in catalysis or in substrate binding. One thiol group, however, lies 5·5 Å from the 3-hydroxyl and is hydrogen-bonded to three of the Asx groups that are binding the sugar. Chemical modification of this buried thiol would disrupt the glucose binding site, which could account for the observation (Otieno et al., 1977) that cyanylation of one of the enzyme's thiols abolishes enzymatic activity.A sulfate molecule is bound to the enzyme by two serine side-chains and its sulfur atom is 5·5 Å from the 6-hydroxyl group of glucose. If the γ-phosphate of ATP binds to this sulfate binding site, it would still be a little too far from the 6-hydroxyl for direct phosphoryl transfer.     

Synthesis and evaluation of novel opioid ligands with a C-homomorphinan skeleton

As the reports about C-homomorphinans with the seven-membered C-ring are much fewer than those of morphinan derivatives with a six-membered C-ring, we attempted to synthesize C-homomorphinan derivatives and to evaluate their opioid activities. C-Homomorphinan 5 showed sufficient binding affinities to the opioid receptors. C-Homomorphinan derivatives possessing the δ address moiety such as indole (NTI-type), quinoline, or benzylidene (BNTX-type) functionalities showed the strongest binding affinities for the δ receptor among the three types of opioid receptors, which indicated that the C-homomorphinan skeleton sufficiently functions as a message-part in the ligand. Although NTI-type compound 8 and quinoline compound 9 with C-homomorphinan scaffold exhibited lower affinities and selectivities for the δ receptor than the corresponding morphinan derivatives did, both the binding affinity and selectivity for the δ receptor of BNTX-type compound 12 with a seven-membered C-ring were improved compared with the corresponding compounds with a six-membered C-ring including BNTX itself. BNTX-Type compound 12 was the most selective δ receptor antagonist among the tested compounds.     

Improved hybridisation potential of oligonucleotides comprising O-methylated anhydrohexitol nucleoside congeners

The hybridising potential of anhydrohexitol nucleoside analogues (HNAs) is well documented, but tedious synthesis of the monomers hampers their development. In a search for better analogues, the synthesis of two new methylated anhydrohexitol congeners 1 and 2 was accomplished and the physico-chemical properties of their respective oligomers were evaluated. Generally, oligonucleotides (ONs) containing the 3′-O-methyl derivative 1 showed a small increase in thermal stability towards complementary sequences as compared to HNA. Compared to the altritol modification, 3′-O-methylation seems to cause a small decrease in thermal stability of duplexes, especially when targeting RNA. These results suggest the possibility of derivatisation of the 3′-hydroxyl group of altritol-containing congeners without significantly affecting the thermal stability of the duplexes. The methyl glycosidic analogues 2 likewise increased the affinity for RNA in comparison with well-known HNA, while at the same time being economically more favorable monomers. However, homopolymers of 2 displayed self-pairing, but not so homopolymers of 1. Upon incorporation of the hexitols within RNA sequences in an effort to induce a beneficial pre-organised structure, the positive effect of the 3′-O-methyl derivative 1 proved larger than that of 2.