De Novo Synthesis and Biological Evaluation of C6″-Substituted C4″‑Amide Analogues of SL0101

In an effort to improve upon the <i>in vivo</i> half-life of the known ribosomal s6 kinase (RSK) inhibitor SL0101, C4″-amide/C6″-alkyl substituted analogues of SL0101 were synthesized and evaluated in cell-based assays. The analogues were prepared using a de novo asymmetric synthetic approach, which featured Pd-π-allylic catalyzed glycosylation for the introduction of a C4″-azido group. Surprisingly replacement of the C4″-acetate with a C4″-amide resulted in analogues that were no longer specific for RSK in cell-based assays

Structure–Activity Relationship Study of the Cleistriosides and Cleistetrosides for Antibacterial/Anticancer Activity

Two known cleistriosides and six known cleistetrosides were synthesized and evaluated for anticancer and antibacterial activities. This study, for the first time, reports anticancer activity and comprehensively the antibacterial activity for these oligosaccharide natural products. In addition, two new unnatural cleistetroside analogues were synthesized and tested. Biological activities for the 10 oligosaccharides against <i>B. subtilis</i> were found to range between 4 and >64 μM and for NCI-H460 human lung cancer epithelial cells between 7.5 and 90.9 μM. Similar activities were found for seven of the oligosaccharides against the NCI panel of 60 cell lines. The degree of acylation and location of the specific acetate groups had significant effects on the anticancer and antibacterial activity of both the cleistriosides and the cleistetrosides

Synthesis and Structure–Activity Relationship Study of 5a-Carbasugar Analogues of SL0101

The Ser/Thr protein kinase, RSK, is associated with oncogenesis, and therefore, there are ongoing efforts to develop RSK inhibitors that are suitable for use <i>in vivo</i>. SL0101 is a natural product that demonstrates selectivity for RSK inhibition. However, SL0101 has a short biological half-life <i>in vivo</i>. To address this issue we designed a set of eight cyclitol analogues, which should be resistant to acid catalyzed anomeric bond hydrolysis. The analogues were synthesized and evaluated for their ability to selectively inhibit RSK <i>in vitro</i> and in cell-based assays. All the analogues were prepared using a stereodivergent palladium-catalyzed glycosylation/cyclitolization for installing the aglycon. The l-cyclitol analogues were found to inhibit RSK2 in <i>in vitro</i> kinase activity with a similar efficacy to that of SL0101, however, the analogues were not specific for RSK in cell-based assays. In contrast, the d-isomers showed no RSK inhibitory activity in <i>in vitro</i> kinase assay

3-Hydroxypyrimidine-2,4-diones as Selective Active Site Inhibitors of HIV Reverse Transcriptase-Associated RNase H: Design, Synthesis, and Biochemical Evaluations

Human immunodeficiency virus (HIV) reverse transcriptase (RT) associated ribonuclease H (RNase H) remains an unvalidated antiviral target. A major challenge of specifically targeting HIV RNase H arises from the general lack of selectivity over RT polymerase (pol) and integrase (IN) strand transfer (ST) inhibitions. We report herein the synthesis and biochemical evaluations of three novel 3-hydroxypyrimidine-2,4-dione (HPD) subtypes carefully designed to achieve selective RNase H inhibition. Biochemical studies showed the two subtypes with an N-1 methyl group (<b>9</b> and <b>10</b>) inhibited RNase H in low micromolar range without siginificantly inhibiting RT polymerase, whereas the N-1 unsubstituted subtype <b>11</b> inhibited RNase H in submicromolar range and RT polymerase in low micromolar range. Subtype <b>11</b> also exhibited substantially reduced inhibition in the HIV-1 INST assay and no significant cytotoxicity in the cell viability assay, suggesting that it may be amenable to further structure–activity relationship (SAR) for identifying RNase H inhibitors with antiviral activity

3‑Hydroxypyrimidine-2,4-dione-5‑<i>N</i>‑benzylcarboxamides Potently Inhibit HIV‑1 Integrase and RNase H

Resistance selection by human immunodeficiency virus (HIV) toward known drug regimens necessitates the discovery of structurally novel antivirals with a distinct resistance profile. On the basis of our previously reported 3-hydroxypyrimidine-2,4-dione (HPD) core, we have designed and synthesized a new integrase strand transfer (INST) inhibitor type featuring a 5-<i>N</i>-benzylcarboxamide moiety. Significantly, the 6-alkylamino variant of this new chemotype consistently conferred low nanomolar inhibitory activity against HIV-1. Extended antiviral testing against a few raltegravir-resistant HIV-1 clones revealed a resistance profile similar to that of the second generation INST inhibitor (INSTI) dolutegravir. Although biochemical testing and molecular modeling also strongly corroborate the inhibition of INST as the antiviral mechanism of action, selected antiviral analogues also potently inhibited reverse transcriptase (RT) associated RNase H, implying potential dual target inhibition. In vitro ADME assays demonstrated that this novel chemotype possesses largely favorable physicochemical properties suitable for further development

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

Double-Winged 3‑Hydroxypyrimidine-2,4-diones: Potent and Selective Inhibition against HIV‑1 RNase H with Significant Antiviral Activity

Human immunodeficiency virus (HIV) reverse transcriptase (RT)-associated ribonuclease H (RNase H) remains the only virally encoded enzymatic function yet to be exploited as an antiviral target. One of the possible challenges may be that targeting HIV RNase H is confronted with a steep substrate barrier. We have previously reported a 3-hydroxypyrimidine-2,4-dione (HPD) subtype that potently and selectively inhibited RNase H without inhibiting HIV in cell culture. We report herein a critical redesign of the HPD chemotype featuring an additional wing at the C5 position that led to drastically improved RNase H inhibition and significant antiviral activity. Structure–activity relationship (SAR) concerning primarily the length and flexibility of the two wings revealed important structural features that dictate the potency and selectivity of RNase H inhibition as well as the observed antiviral activity. Our current medicinal chemistry data also revealed that the RNase H biochemical inhibition largely correlated the antiviral activity