Synthesis of <i>cis</i>- and <i>trans</i>-α‑l‑[4.3.0]Bicyclo-DNA Monomers for Antisense Technology: Methods for the Diastereoselective Formation of Bicyclic Nucleosides

Two α-l-<i>ribo</i>-configured bicyclic nucleic acid modifications, represented by analogues <b>12</b> and <b>13</b>, which are epimeric at C₃′ and C₅′ have been synthesized using a carbohydrate-based approach to build the bicyclic core structure. An intramolecular l-proline-mediated aldol reaction was employed to generate the <i>cis</i>-configured ring junction of analogue <b>12</b> and represents a rare application of this venerable organocatalytic reaction to a carbohydrate system. In the case of analogue <b>13</b>, where a <i>trans</i>-ring junction was desired, an intermolecular diastereoselective Grignard reaction followed by ring-closing metathesis was used. In order to set the desired stereochemistry at the C₅′ positions of both nucleoside targets, a study of diastereoselective Lewis acid mediated allylation reactions on a common bicyclic aldehyde precursor was carried out. Analogue <b>12</b> was incorporated in oligonucleotide sequences, and thermal denaturation experiments indicate that it is destabilizing when paired with complementary DNA and RNA. However, this construct shows a significant improvement in nuclease stability relative to a DNA oligonucleotide

Synthesis of <i>cis</i>- and <i>trans</i>-α‑l‑[4.3.0]Bicyclo-DNA Monomers for Antisense Technology: Methods for the Diastereoselective Formation of Bicyclic Nucleosides

Two α-l-<i>ribo</i>-configured bicyclic nucleic acid modifications, represented by analogues <b>12</b> and <b>13</b>, which are epimeric at C₃′ and C₅′ have been synthesized using a carbohydrate-based approach to build the bicyclic core structure. An intramolecular l-proline-mediated aldol reaction was employed to generate the <i>cis</i>-configured ring junction of analogue <b>12</b> and represents a rare application of this venerable organocatalytic reaction to a carbohydrate system. In the case of analogue <b>13</b>, where a <i>trans</i>-ring junction was desired, an intermolecular diastereoselective Grignard reaction followed by ring-closing metathesis was used. In order to set the desired stereochemistry at the C₅′ positions of both nucleoside targets, a study of diastereoselective Lewis acid mediated allylation reactions on a common bicyclic aldehyde precursor was carried out. Analogue <b>12</b> was incorporated in oligonucleotide sequences, and thermal denaturation experiments indicate that it is destabilizing when paired with complementary DNA and RNA. However, this construct shows a significant improvement in nuclease stability relative to a DNA oligonucleotide

Improving the Affinity of SL0101 for RSK Using Structure-Based Design

Enhanced activity of the Ser/Thr protein kinase, RSK, is associated with transformation and metastasis, which suggests that RSK is an attractive drug target. The natural product SL0101 (kaempferol 3-<i>O</i>-(3″,4″-di-<i>O</i>-acetyl-α-l-rhamnopyranoside)) has been shown to be an RSK selective inhibitor. However, the <i>K</i>_i for SL0101 is 1 μM with a half-life of less than 30 min <i>in vivo</i>. To identify analogues with improved efficacy we designed a set of analogues based on the crystallographic model of SL0101 in complex with the RSK2 N-terminal kinase domain. We identified an analogue with a 5″-<i>n</i>-propyl group on the rhamnose that has >40-fold improved affinity for RSK relative to SL0101 in an <i>in vitro</i> kinase assay. This analogue preferentially inhibited the proliferation of the human breast cancer line, MCF-7, versus the normal untransformed breast line, MCF-10A, which is consistent with results using SL0101. However, the efficacy of the 5″-<i>n</i>-propyl analogue to inhibit MCF-7 proliferation was only 2-fold better than for SL0101, which we hypothesize is due to limited membrane permeability. The improved affinity of the 5″-<i>n</i>-propyl analogue for RSK will aid in the design of future compounds for <i>in vivo</i> use