Recent reports from several laboratories have pointed to the fact that folylpolyglutamate synthetase (FPGS), the enzyme responsible for the conversion of endogenous reduced folates as well as a variety of folate antagonists to their γ-polyglutamylated forms, has a high degree of side chain specificity but is relatively tolerant of structural changes in rings A and B, the 'bridge region' and the phenyl ring (Figure 1). With regard to ring A, for example, it has been shown that replacement of the 2-amino group by hydrogen in the N⁵-methyl-, N⁵-ethyl-, N⁵-allyl-, and N⁵-propargyl-substituted derivatives of 5,8-dideazafolic acid results in a minimal change in either the Kₘ or Vₘₐₓ for γ-diglutamate formation by mouse liver FPGS. Similar results were obtained for replacement of the 2-amino group by hydrogen in 10-oxafolic acid and 10-thiafolic acid, and for replacement of the 2-amino group by hydrogen or methyl in aminopterin. We postulated that since changes in the 2-substituent at in ring A are well tolerated, the carbon itself at position 2 may not be absolutely required for binding to the enzyme. To test this hypothesis we prepared the heretofore undescribed compound N-[4-[[(2-amino-3-carbamoylpyrazin-5-yl)methyl]amino]benzoyl]-glutamic acid (1), which may be viewed as a folic acid analogue in which both the 2-amino group and C2 have been deleted. Also synthesized was N-[4-[[(2-amino-3-carbamoylpyrazin-5-yl)methyl]formamido]benzoyl]-L-glutamic acid (2), the corresponding ring-opened analogue of N⁵-formylfolic acid. Compound 1 inhibited the growth of L1210 murine leukemic cells in culture with an IC₅₀ of 5 μM and was comparable to folic acid as a substrate for FPGS, providing the first demonstration that an intact A ring in folate analogues is not an absolute requirement for FPGS substrate activity. We believe these results are a timely and potentially exploitable lead for the design of other biologically active folate analogues. It is now well-established that inhibition of the enzyme HMG-CoA reductase (HMGR) is an effective means for lowering plasma total and LDL-cholesterol in hypercholesterolemic patients. However, the long-term safety of these agents is still unproven. Although recent clinical experience with lovastatin (1) has indicated that it is well-tolerated in man, some adverse reactions have been noted; particularly, elevated liver enzymes, sleep disturbances, and myositis. Recently, there has been considerable controversy in the literature regarding both the nature and existence of tissue (liver) selectivity for various HMGR inhibitors, and whether confining their action to the liver would reduce the incidence of adverse reactions. The initial report describing tissue selectivity for pravastatin (2) suggested that pravastatin and lovastatin were equipotent at inhibiting cholesterol biosynthesis in cultured rat hepatocytes, but pravastatin was 100 times less potent than lovastatin at inhibiting biosynthesis in human skin fibroblasts. This selectivity was further supported by ex vivo rat studies, which demonstrated that pravastatin inhibited cholesterol biosynthesis only in lipoprotein-producing organs (liver and intestine), whereas lovastatin and mevastatin (compactin) also inhibited cholesterol biosynthesis significantly in kidney, lung, spleen, prostate, and testis. The assertion that pravastatin is more tissue selective than lovastatin has been disputed, however, on the basis of measurements of peripheral drug distribution employing a bioassay as well as the uptake and tissue distribution of radiolabeled drug. More recently, other HMGR inhibitors have been reported to display liver selectivity. It has been proposed that tissue selectivity is influenced primarily by the relative lipophilicity of the drugs, with the relatively more hydrophilic compounds showing higher liver selectivity. Since we had prepared HMGR inhibitors possessing considerable variation in structure and lipophilicity during the course of our program in this area, we decided to test this hypothesis directly. Thus, we compared a selection of potent inhibitors possessing a broad range of calculated lipophilicities (CLOGP) for their abilities to inhibit sterol synthesis in tissue cubes derived from rat liver, spleen, and testis. The results of these studies are the subject of this report.