Novel Squalene-Hopene Cyclase Inhibitors Derived from Hydroxycoumarins and Hydroxyacetophenones

Abstract

One of the most intensively studied enzymes of sterol biosynthesis, oxidosqualene cyclase (OSC), catalyzes the conversion of an acyclic compound, 2,3-oxidosqualene, to the first cyclic intermediate along the pathway. This is lanosterol in all non-photosynthetic organisms, and cycloartenol in plants.1) While several mammalian OSCs were being isolated, characterized, cloned and sequenced, 2-9) hundreds of OSC inhibitors have been designed and tested [10][11][12][13][14] as potential anti-fungal 15) or cholesterol-lowering drugs. 16) Recently, a novel series of orally active inhibitors have been tested on human liver microsomal OSC, and their effectiveness as cholesterol-lowering drugs has been evaluated in hyperlipidemic hamsters.17) OSC inhibitors are also under investigation as potential anti-trypanosomal agents. 18,19) The design of new OSC inhibitors received a further boost when the complete structure of a squalene hopene cyclase (SHC) was elucidated. 20) This bacterial enzyme, isolated from the thermophilic bacterium Alicyclobacillus acidocaldarius, proved particularly interesting because its sequence revealed a remarkable degree of homology and partial identity with eukaryotic OSCs. 21,22) SHC may therefore be used as a model to predict how newly designed inhibitors may interact with OSCs. Recently, the interaction of several new inhibitors of human OSC 17) with the active site of SHC was investigated by co-crystallization experiments.23) Because comparative studies on the two enzyme types 24,25) have shown close correspondence of their inhibitor activities, we recently investigated a group of meroterpenoids that proved to be excellent inhibitors of SHC.26) The basic structure of bioactive oxyprenylcoumarins is derived from umbelliprenine (7-farnesyloxycoumarin) by the insertion of either a tetrahydrofuran unit (farnesylferol C, 1) or 1-2 oxiran rings (2, 3) (Fig. 1). While farnesyferol C (IC 50 7.0 mM) is a naturally occurring compound, umbelliprenine-10Ј,11Ј-monoepoxyde (2) (IC 50 2.5 mM) and diepoxyde (3) (IC 50 1.5 mM) have been previously obtained by synthesis. 26)This encouraging start prompted us to extend the study of structure-activity relationships by modifying both the heterocyclic nucleus and the side chain, hopefully to improve molecular recognition. Results and DiscussionWe proceeded towards molecular simplification and also covered a few isosters, i.e. thiocoumarin and quinolindione derivatives. 2-and 4-thiocoumarin nuclei were accessed by a published procedure, 27,28) while 2,4-quinolinediol was commercially available. S-Geranylthiocoumarins 7 and 8 were prepared via a Mitsunobu reaction.29) 4-O-Geranyl-quinolin-2-one (10) was prepared according to Grundon. 30)The isosters synthesized by us (7-10) showed lower inhibitory activities compared to either the O-geranylcoumarins or the w-epoxy derivative 6. A shorter side chain, as in aurapten 31) (7-geranyloxycoumarin, 5) and 6Ј,7Ј-epoxyaurapten 32) (6) or prenyletin 33,34) (4) was also deleterious for the inhibitory activity.All relevant struct...

Chemistry and Biological Activity of Natural and Synthetic Prenyloxycoumarins †

“…Many related compounds have been described; starting from aesculetin (6,7-dihydroxycoumarin) and daphnetin (7,8- of squalene-hopene cyclase (SHC) inhibitors [261][262]. This bacterial enzyme, isolated from Alicyclobacillus acidocaldarius, is used as a convenient model to identify inhibitors of oxidosqualene cyclase (OSC) because comparative studies have shown that inhibitor activities on the two enzyme types stand in close correspondence.…”

Umbelliferone aminoalkyl derivatives as inhibitors of human oxidosqualene-lanosterol cyclase

“…Coumarin derivatives (Figure 2) and the OSC substrate, 2,3-oxidosqualene (OS), were synthesized as previously reported [10]. The 3-acyl-4-hydroxycoumarin 4 is a new compound prepared in three steps: 1) acylation of 4-hydroxycoumarin with 10-undecenoyl chloride [11]; 2) Oxidative demolition of the terminal double bond obtaining the 10-formyl derivative [12]; 3) reductive amination with excess allylmethylamine [12].…”

“…Incorporation of [2][3][4][5][6][7][8][9][10][11][12][13][14] C] acetate into non-saponifiable lipids of human keratinocytes and mouse 3T3 fibroblasts Cells were seeded in 24-well plastic clusters. Each well received 7 £ 10 4 cells suspended in 950 mL DMEM (Dulbecco-modified Eagle medium) containing 10% (v/v) lipid-depleted serum [20].…”

“…The effects of a series of umbelliferone aminoalkyl derivatives ( Figure 2) on sterol biosynthesis was studied in mouse 3T3 fibroblasts, a cell line we previously used with other OSC inhibitors [26,27], and human keratinocytes incubated with [2][3][4][5][6][7][8][9][10][11][12][13][14] C] acetate by determining the amounts of radioactive label taken up by the biosynthetic intermediates.…”

Long‐Chain 3‐Acyl‐4‐hydroxycoumarins: Structure and Antibacterial Activity

“…Provided these crucial features were presumed that replacing the 4-hydroxycoumarin with the 2H-indene-1,3-dione nucleus 3a had no effect on the antimicrobial activity. We prepared a large number of acyl derivatives of which only the most active are described below (1a -d), namely those bearing an undec-10-enoyl-(1a) [21], undec-10-ynoyl-(1b), palmitoyl-(1c), or (Z)-octadec-9-enoyl-(1d) chain (Fig. 1).…”