12th International HIV Drug Resistance Workshop


10–14 June 2003, Cabo del Sol, Los Cabos, Mexico


SYNTHESIS AND ANTI-HIV ACTIVITY OF ENANTIOMERICALLY PURE D-FDOC

Antivir Ther. 2003; 8:S7 (abstract no. 4)

S Mao1, M Bouygues1, DC Liotta1, RF Schinazi2, C Welch3, M Biba3, and J Chilenski3
1Department of Chemistry, Emory University, Atlanta, Ga.; 2Veterans Affairs Medical Center and Department of Pediatrics, Emory University School of Medicine, Decatur, Ga.; and 3Merck Research Laboratories, Division of Merck & Co., Inc., Rahway, NJ, USA

The potential of 1',3'-dioxolanyl nucleosides as anti-HIV drugs has been recognized for some time. In the mid-1990s, we both enantiomers of 2',3'-dideoxy-5-fluoro- oxacytidine (FDOC) were synthesized. Although both enantiomers exhibited good potency against HIV, they both appeared to be too toxic to be used clinically. Subsequent to these initial studies, we discovered that the sample of the less toxic D-enantiomer that was tested actually contained 3–5% of its significantly more toxic L-counterpart. This then raised the interesting question as to whether the observed toxicity was inherent to D-FDOC or resulted from the presence of small quantities of its more toxic enantiomer. To answer this question, we used preparative chiral chromatography to obtain several grams of optically pure D- and L-FDOC, respectively. With these two enantiomers in hand, we could, for the first time, unambiguously evaluate their anti-HIV activity, cytotoxicity and resistance profile. The results of these studies indicated that D-FDOC not only showed excellent potency (EC50 and EC90 values in primary human lymphocytes infected with HIV-1LAI are 0.04 µM and 0.26 µM, respectively) and low toxicity (>100 µM in uninfected primary human lymphocytes), but also exhibited no cross resistance to lamivudine, zidovudine or nevirapine. In addition, in primary mouse bone marrow cells, D-FDOC showed no increase in lactic acid production even at 300 µM. In contrast, treatment with either LFDOC and zalcitabine resulted in a >300-fold increase in lactic acid production relative to untreated control. Furthermore, in HepG2 cells (5-day assay), D-FDOC displayed no toxicity when tested up to 100 µM, whereas its L-counterpart demonstrated significant toxicity at 1.4 µM. While these data, taken in aggregate, clearly indicate that our original toxicity determinations were compromised by the presence of small quantities of the toxic L-enantiomer, they also suggest that clinical evaluations of D-FDOC should only be performed with materials that contain very little, if any, of the L-enantiomer. Herein, we describe a synthetic approach that employs a tandem kinetic resolution/ chiral salt crystallization protocol for preparing the D-enantiomer of FDOC in high enantiopurity. In addition, we report conditions that allow for the racemization and recycling of the unwanted butyrate ester of the L-enantiomer of FDOC.

PRESENTING AUTHOR: DC Liotta

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2003-07-08
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