SYNTHESIS AND ABSOLUTE-CONFIGURATIONS OF THE NATURALLY-OCCURRING 3-METHYLMUCONOLACTONE AND 4-METHYLMUCONOLACTONE - X-RAY STRUCTURES OF (S)-1-PHENYLETHYLAMMONIUM SALTS AND AN 8-BROMO-1-METHYLMUCONODILACTONE

(+/-)-3-Methylmuconolactone (+/-)-4 is resolved by fractional crystall isation of the (S)-(-)-1-phenylethylammonium salts. The X-ray crystal structures of both salts are determined. Salt A (Fig, 1) gives (S)-(-) -3-methylmuconolactone 4, which is identical to the lactone from fungi , The lactone is converted with bromine into the bromo dilactone 5 and thence with tributyltin hydride into the (-)-1-methylmuconodilactone 6. This dilactone with aqueous sodium hydroxide gives (S)-(+)-4-methyl muconolactone 3, which is identical to the lactone from bacteria, toge ther with (S)-(-)-3-methylmuconolactone 4, The X-ray structure of the bromo dilactone 5 (Fig, 3) confirms the absolute configurations of bot h the fungal and bacterial muconolactones, (S)-(+)-4-Methylmuconolacto ne 3 gives the corresponding (-)-bromo dilactone 9, which is also redu ced with tributyltin hydride to yield the (-)-1-methylmuconodilactone 6. The isomeric bromo dilactones (+/-)-5 and 9 are similarly converted into the dibromo dilactones (+/-)-8 and 11 via the corresponding 2-br omomuconolactones (+/-)-7 and 10, respectively. Disodium 3-methyl-cis, cis-muconate 17 is prepared non-enzymically by treatment of 3-methylmu conic anhydride 16 with 2 mol equiv, of aqueous sodium hydroxide, Unex pectedly, the salt 17 rapidly gives 3-methyl-2-cis,4-trans-muconate ev en in weakly alkaline solutions, Contrary to an earlier report, at pD 6.5 the salt 17 is converted at approximately equal rates into 3-methy l-2-cis,4-trans-muconic acid 18 and (+/-)-3-methylmuconolactone (+/-)- 4.