Cyclophostin a structurally unique and potent naturally occurring acetyl cholinesterase (AChE)

Cyclophostin a structurally unique and potent naturally occurring acetyl cholinesterase (AChE) inhibitor and its unnatural diastereomer were prepared in 6 actions and 15% overall yield from hydroxymethyl butyrolactone. isolated from a fermentation solution NSC-207895 (XI-006) of (strain NK901093).1 The natural product 1 showed potent inhibition of acetyl cholinesterase (AChE) from your housefly (CSMA strain) and the brown herb hopper with reported IC50 of 7.6 ×10?10 M. The structure of cyclophostin was first assigned by spectroscopic methods and then confirmed by single crystal X-ray diffraction studies as a bicyclic structure with a seven-membered cyclic enol-phosphate triester fused to a butyrolactone ring. You will find chirality centers at both C3a and the phosphorus atom (6). The complete configurations were determined to be 3aisomer (H and OMe) 5b was 10 fold more active (IC50 of 3 μM human AChE) than the isomer 5a (IC50 of 30 μM human AChE). Since the natural product has the (H NSC-207895 (XI-006) and OMe) configuration the unnatural isomer may well prove more potent. In order to accurately compare the activity of cyclophostin the phosphonate analog and their diastereomers with a detailed kinetic analysis we needed affordable quantities of the natural product. Furthermore we proposed that cyclophostin would be an excellent precursor for the synthesis of the family of cyclipostins. Herein we statement the first synthesis of (±) cyclophostin and conversion into (±) cyclipostin P. A retrosynthetic analysis (Plan 1) of the bicyclic phosphate 1 suggested that this cyclic enolphosphate NSC-207895 (XI-006) could be created either by condensation of the acetyl group (as the enol) with a phosphoric acid via intermediate 8 (route A) or conversely condensation of the primary alcohol with an enolphosphoric acid via intermediate 10 (route B). Both intermediates can be created by C-acylation of derivatives of hydroxymethyl lactone 6. The lactone 6 and various derivatives are available in the racemic CD1B modification11 and either enantiomer.12 It was thought necessary to protect the hydroxyl of lactone 6 prior to C-acetylation to avoid complications arising from cyclization of the acetyl lactone 11 to the hemiketal 12.12b The most expedient route would be to introduce NSC-207895 (XI-006) the phosphate early in the synthesis simultaneously protecting the hydroxyl group. Plan 1 Cyclophostin Retrosynthetic Analysis. The racemic hydroxy lactone 6 was prepared using published methods.11 The hydroxyl was phosphorylated using dimethyl bromophosphate prepared by reaction of trimethyl phosphite with bromine to give the phosphate 7 (Plan 2). The phosphorylated butyrolactone 7 was deprotonated with one equivalent of LiHMDS in THF and the producing enolate was acylated with acetyl chloride.4a 5 Initially mixtures of the acetyl lactone 14 and the enolacetate 13 were observed so an excess of acetyl chloride was added to ensure the complete acylation giving enolacetate 13 in 65% yield as a mixture NSC-207895 (XI-006) of two geometrical isomers. The geometrical isomers could be separated but were generally carried through to the next step as a mixture. Deacetylation of enolacetates 13 was achieved using a catalytic amount of DMAP in MeOH to give the acetyl lactone 14 in 62% yield. Plan 2 Synthesis of Main Phosphate. The successful C-acylation of the lactone 7 was both gratifying and somewhat surprising. It is well known that this enolates derived from γ-phosphoryloxy carboxylates cyclize to form cyclopropanes.13 Indeed when the acyclic γ-phosphoryloxy carboxylate 15 was treated with LiHMDS and acetyl chloride (plan 3) the only isolable product was the cyclopropane 16. In contrast a solution the enolate of butyrolactone 7 was stable in the absence of an external electrophile up to ?20 °C for one hour. At higher temperatures decomposition to intractable products was observed. Plan 3 Formation of Cyclopropanes. With the desired 2-acetyl butyrolactone intermediate 14 in hand the final step of the cyclophostin synthesis was explored (Plan 4). The intermediate 14 was demethylated using one equivalent of sodium iodide in refluxing acetonitrile answer to give the corresponding sodium salt in quantitative yield.14 The sodium salt was protonated using amberlite? (sulfonic acid) resin to yield the phosphoric acid 8. Attempted cyclization via intramolecular.