The syntheses of the enantiomerically pure, carnitine-related /?-lactones 10 and 12 starting from various carnitine precursors of opposite configuration (or carnitine itself) are described. (R)-3-Chlorocarnitine (20) has also been directly prepared from (S)-carnitine (14) and has been cyclized to 12 by a second inversion of configuration of the stereogenic centre. By nucleophilic attack at the carbony1 carbon, the /?-lactone carnitine derivatives have been converted into esters, amides and guanidino congeners. Following this route, it is possible to obtain the biologically active isomer (R)-carKeywords asymmetric ring-opening -carnitinecyclizations /?-lactones * nucleophilic substitutions

1 in practically quantitative yield (720 mg, > 99 "h). 6: A solution of 5 (1.5 g, 4.47 mmol) in H,O was transferred onto Amberlite IRA-402 (30 g. activated as HCO;) at 5'C and eluted with cold water ( 5 C) The eluate was allowed to stand for 4 h at room temperature to give, after water evaporation under vacuum, a crude product, which was taken up into CH,CN and filtered. The filtrate was evaporated to dryness to give 6 (0.855 g, XO%) as a white solid. M.p. 160°C (decomp.): [n], = -24.7 ( c = 1 in MeOH); 'H NMR (300 MHz. D,O, 25°C)-6 = 5. IH). 3.98-3.89 (m, 3H), 3.54-3.46 (dd. ' J = 16.8 HI,

The syntheses of the enantiomerically pure, carnitine‐related β‐lactones 10 and 12 starting from various carnitine precursors of opposite configuration (or carnitine itself) are described. (R)‐3‐Chlorocarnitine (20) has also been directly prepared from (S)‐carnitine (14) and has been cyclized to 12 by a second inversion of configuration of the stereogenic centre. By nucleophilic attack at the carbonyl carbon, the β‐lactone carnitine derivatives have been converted into esters, amides and guanidino congeners. Following this route, it is possible to obtain the biologically active isomer (R)‐carnitine (1) starting from the otherwise useless industrial by‐product (S)‐carnitine (14). Nucleophilic attack by selected ambidient nucleophiles at the β‐carbon of the same β‐lactone derivatives results in a second inversion of configuration of the stereogenic centre. Besides aminocarnitine (3), chiral acetylcarnitine (2) and acetylthiocarnitine (5) have been synthesized in homochiral forms following this latter procedure.

Tonnen von ungenutztem (s)‐Carnitinamid 1 die bei der industriellen Herstellung des biologisch aktiven, pharmazeutisch bedeutsamen (R‐Isomers 3 anfallen, können nun zu diesem umgesetzt werden. In formal fünf Stufen gelingt die Isomerisierung über das β‐Lacton 2 in einer Gesamtausbeute von 80%.

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