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Synlett 2005(17): 2676-2678  
DOI: 10.1055/s-2005-917096
LETTER
© Georg Thieme Verlag Stuttgart · New York

A Synthetic Approach to Sporotricale Methylether

Sabrina Dallavalle*a, Raffaella Nanneia, Lucio Merlinia, Adriana Bavab, Gianluca Nasinib
a Dipartimento di Scienze Molecolari Agroalimentari, Sezione di Chimica, Università di Milano, Via Celoria 2, 20133 Milano, Italy
e-Mail: sabrina.dallavalle@unimi.it;
b CNR, ICRM, Dipartimento di Chimica, Materiali ed Ingegneria Chimica, Politecnico di Milano, Via Mancinelli 7, 20131 Milano, Italy
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Publication History

Received 11 July 2005
Publication Date:
05 October 2005 (online)

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Abstract

A synthetic approach to sporotricale methylether, a metabolite of the fungus Sporotrichum laxum with inhibitory activity against Helicobacter pylori, is described. The synthesis relies on the condensation of 13-hydroxy-10-oxotetradecanal, prepared via reaction of a sulfone-activated moiety with valerolactone, with diethyl 3,5-dimethoxyphthalide-7-phosphonate.

Key words

natural products - total synthesis - sulfones - condensation - hydrogenation

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Preparation of E / Z 3-(13-Hydroxy-10-oxo-tridecyl-idene)-5,7-dimethoxy-3 H -isobenzofuran-1-one ( 13).
To a stirred solution of phosphonate 4 (0.024 g, 0.12 mmol) and aldehyde 5 (0.024 g, 0.12 mmol) in dry THF (0.8 mL), NaH (7.4 mg of a 60% dispersion in mineral oil; 0.154 mmol) was added and the mixture stirred under nitrogen at r.t. for 5 d. After addition of H2O, the organic layer was separated and evaporated in vacuo to give a residue which was purified by preparative layer chromatography (PLC) using 1:1 hexane-EtOAc as eluent to afford the Z-isomer 13 as a solid (11 mg, 24%), mp 79-81 °C and the E-isomer as an oil, (8 mg, 18%). 1 H NMR (CDCl3): δ (Z-isomer) = 1.22 (3 H, d, J = 6.2 Hz, H-14′), 2.00-1.20 (14 H, m, 7 × CH2), 2.45 and 2.35 (4 H, m, H-9′ and H-11′), 2.51 (2 H, dt, J = 7.8, 7.5 Hz, H-2′), 3.85 (1 H, m, H-13′), 3.92 (3 H, s, OMe), 3.97 (3 H, s, OMe), 5.55 (1 H, t, J = 7.8 Hz, H-1′), 6.70 and 6.45 (2 H, br d, J = 1.8 Hz, H-4 and H-6); δ (E-isomer) = 1.22 (3 H, d, J = 6.2 Hz, H-14′), 2.00-1.20 (14 H, m, 7 × CH2), 2.48 and 2.33 (4 H, m, H-9′ and H-11′), 2.49 (2 H, dt, J = 7.8, 7.5 Hz, H-2′), 3.87 (1 H, m, H-13′), 3.93 (3 H, s, OMe), 3.98 (3 H, s, OMe), 5.79 (1 H, t, J = 7.8 Hz, H-1′), 6.80 and 6.47 (2 H, br d, J = 1.8 Hz, H-4 and H-6). MS (EI): m/z (%) = 400 (41), 345 (15), 219 (80), 111 (90), 55 (100).
Preparation of (±) Sporotricale Methylether(2).
Compound 13 (12 mg) dissolved in MeOH (5 mL) was hydrogenated at r.t. with 10% Pd/C (3 mg) for 20 min. PLC of the residue in 50:50 hexane-EtOAc gave 6 mg (50%) of 2, mp 94-96 °C. 1H NMR (CDCl3): δ (hemiketal) = 1.22 (3 H, d, J = 6.2 Hz, H-14′), 2.50-1.20 (22 H, m, 11 × CH2), 3.83 (1 H, m, H-13′). 3.90 (3 H, s, OMe), 3.95 (3 H, s, OMe), 5.29 (1 H, br dd, J = 7.2, 4.0 Hz, H-7), 6.42 and 6.40 (2 H, br d, J = 1.7 Hz, H-4 and H-6); 1H NMR (acetone-d 6):
δ (hydroxyketone) = 1.10 (3 H, d, J = 7.2 Hz, H-14′), 2.00-1.20 (18 H, m, 9 × CH2), 2.53 and 2.44 (4 H, t, J = 7.5 Hz, H-9′ and H-11′), 3.66 (1 H, m, H-13′), 3.92 (3 H, s, OMe), 3.93 (3 H, s, OMe), 5.35 (1 H, br dd, J = 7.6, 3.6 Hz, H-7), 6.71 and 6.59 (2 H, br d, J = 1.7 Hz, H-4 and H-6). 13C NMR (acetone-d 6): δ = 210.01 (C-10′), 166.92 (C-1), 166.73, 159.49, 155.30, 106.45, 98.53, 98.02, 79.22 (C-3), 66.06 (C-13′), 55.57 (OMe), 55.30 (OMe), 42.10-23.60 (11 × CH2), 21.87. MS (EI): m/z (%) = 403 (75) [MH+], 402 (44) [M+], 207 (34), 193 (55), 111 (55), 55 (100).
The 1H NMR spectrum of this product was identical with that of natural sporotricale methylether. HPLC comparison: natural 2, column LiChroCART 250-4 SiO2 (Merck), eluent hexane-EtOAc (1:3), retention time (t R) = 14.72 min; column Chiral Daicel OB, eluent hexane-i-PrOH (9:1) t R = 3.19; synthetic 2, column LiChroCART 250-4 SiO2 (Merck), t R = 14.78, column Chiral Daicel OB, t R = 3.19 (48.6%); 10.91 (51.4%). Analyses were performed using a Merck-Hitachi l-4000 instrument equipped with a l-6000A pump and a UV detector (250 nm); flow rate 0.5 mL/min.

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Nasini, G. et al. manuscript in preparation.