Mycophenolic acids

Although it may be considered as a meroterpenoid (see Chapter 5) mycophenolic acid (4.32) is discussed here because its structure reveals the interaction between polyketides and terpenoids. A metabolite of a Penicillium species, which was probably mycophenolic acid, was first described by Gosic in 1896. It was more firmly characterized by Alsberg and Black in 1913 as a metabolite of 

Biosynthetic studies showed that the aromatic ring was formed from a poly-ketide whilst the side chain was derived from the mevalonate terpenoid pathway. The C-5 O-methyl and C-4 methyl groups were derived from methionine. The high incorporation of 4,6-dihydroxy-2,3-dimethyl-[l- C]benzoic acid (4.37) suggested that the methylation at C-4 occurred at the polyketide stage prior to the formation of the phthalide. 5,7-Dihydroxy-4-methyl-[7- C]phthalide (4.38) and its 6-farnesyl analogue were also incorporated eiSciently into mycophenolic acid. The farnesyl precursor was detected as a metabolite of P. brevi-compactum and shown to be formed from 5,7-dihydroxy-4-methyl-[7- C]phthalide by a trapping 

Mycophenolic acid has anti-fungal, anti-bacterial and anti-viral activity. It is a potent inhibitor of inositol monophosphate dehydrogenase and guanosine monophosphate synthase and hence of nucleotide biosynthesis. Mycophenolic acid has a powerful immunosuppressive activity and the morpholine amide (CellCept ) is used to prevent rejection of organ transplants and has been recommended for the treatment of psoriasis. 

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Succinic acid Turpentine oil Mycophenolic acid Pencillium brevi, compactum... 

The active metabolite of this drug is mycophenolic acid (MPA), which inhibits IMPDH, too. MPA is metabolized in vivo by glucuronidation. It has to be noted that its acyl glucuronide inhibits EVDPDH with similar potency compared to the parent compound. 

C4H2CI2O2 87-56-9) see Amezinium metilsulfate mycophenolic acid chloride... 

These agents generally are considered to be adjuvant to the calcineurin inhibitors or possibly sirolimus. The antiproliferatives azathioprine and the mycophenolic acid (MPA) derivatives inhibit T cell proliferation. 

Mycophenolate mofetil was approved by the FDA in 1995, and enteric-coated mycophenolic acid was approved in 2004. Both agents are considered to be adjunctive immunosuppressants. Mycophenolic acid acts by inhibiting inosine monophosphate deydrogenase, a vital enzyme in the de novo pathway of purine synthesis. Inhibition of this enzyme prevents the proliferation of most cells that are dependent on the de novo pathway for purine synthesis, including T cells.7,11,26-28... 

Mycophenolate mofetil is available in 250 mg capsules and 500 mg tablets, an oral suspension (100 mg/mlL, in cherry syrup), and an injectable.11 Usual doses of mycophenolate mofetil range from 1000 to 3000 mg/day in two to four divided doses. The conversion between oral and IV mycophenolate mofetil is 1 1. Enteric-coated mycophenolic acid is available in 180 and 360 mg tablets. For conversion between mycophenolate mofetil and enteric-coated MPA, 1000 mg mycophenolate mofetil is equivalent to 720 mg enteric-coated MPA.26,29 The recommended starting dose of enteric-coated mycophenolic acid is 720 mg given twice daily.11 It appears that conversion of mycophenolate mofetil to enteric-coated mycophenolic acid is safe, but more studies are needed to determine the exact role of enteric-coated MPA in the immunosuppressive armamentarium. Mycophenolic acid trough concentrations can be monitored, but they are not recommended routinely. 

The most common adverse events associated with these agents are GI (18% to 54%, namely, diarrhea, nausea, vomiting, and gastritis) and myelosuppression (20% to 40%).7,11,26-28 Despite its enteric coating, to date, mycophenolic acid has shown no significant benefit in terms of reduction in GI adverse events compared with mycophenolate mofetil in renal transplant recipients.26... 

We saw in Chapter 3 that bisubstrate reactions can conform to a number of different reaction mechanisms. We saw further that the apparent value of a substrate Km (KT) can vary with the degree of saturation of the other substrate of the reaction, in different ways depending on the mechanistic details. Hence the determination of balanced conditions for screening of an enzyme that catalyzes a bisubstrate reaction will require a prior knowledge of reaction mechanism. This places a necessary, but often overlooked, burden on the scientist to determine the reaction mechanism of the enzyme before finalizing assay conditions for HTS purposes. The importance of this mechanistic information cannot be overstated. We have already seen, in the examples of methotrexate inhibition of dihydrofolate, mycophenolic acid inhibiton of IMP dehydrogenase, and epristeride inhibition of steroid 5a-reductase (Chapter 3), how the [5]/A p ratio can influence one s ability to identify uncompetitive inhibitors of bisubstrate reactions. We have also seen that our ability to discover uncompetitive inhibitors of such reactions must be balanced with our ability to discover competitive inhibitors as well. 

Even fully substituted aromatic compounds can be prepared utilizing the Mi-chael/Dieckmann strategy. As reported by Covarrubias-Zuniga and coworkers (Scheme 2.32) [67], reaction of the anion of l-allyl-l,3-acetonedicarboxylate (2-138) and the ynal 2-139 afforded the intermediate 2-140 which led to the resorcinol 2-142 with spontaneous aromatization under acidic conditions via 2-141 in an overall yield of 32 %. 2-142 was transformed into mycophenolic acid (2-143) in only a few additional steps [68]. 

Patino B, Medina A, Domenech M, Gonzalez-Jaen MT, Jimenez M and Vazquez C. 2007. Polymerase chain reaction (PCR) identification of Penicillium brevicompactum, a grape contaminant and mycophenolic acid producer. Food Addit Contam 24(2) 165-172. 

Phenomenex (see 2006 Catalog, SPE products) Strata-X Polar functionalized styrene-divinylbenzene polymer Reversed phase with weakly acidic, hydrogen bond donor, acceptor, and dipolar interactions Cetirizine (76) pyridoxine (77) omeprazole (78) mycophenolic acid (79) 25-hydroxy-vitamin D3 (80)... 

In addition to the aforementioned allenic steroids, prostaglandins, amino acids and nucleoside analogs, a number of other functionalized allenes have been employed (albeit with limited success) in enzyme inhibition (Scheme 18.56) [154-159]. Thus, the 7-vinylidenecephalosporin 164 and related allenes did not show the expected activity as inhibitors of human leukocyte elastase, but a weak inhibition of porcine pancreas elastase [156], Similarly disappointing were the immunosuppressive activity of the allenic mycophenolic acid derivative 165 [157] and the inhibition of 12-lipoxygenase by the carboxylic acid 166 [158]. In contrast, the carboxyallenyl phosphate 167 turned out to be a potent inhibitor of phosphoenolpyruvate carboxylase and pyruvate kinase [159]. Hydrolysis of this allenic phosphate probably leads to 2-oxobut-3-enoate, which then undergoes an irreversible Michael addition with suitable nucleophilic side chains of the enzyme. 

Scheme 7.7 Glucuronidation of mycophenolic acid with liver homogenate.

Shipkova, M., Armstrong, V.M., Wieland, E., Niedmann, P.D., Schiitz, E., Brenner-WeiC, G., Voihsel, M., Braun, E. and Oellerich, M., Identification of glucoside and carboxyl-linked glucuronide conjugates of mycophenolic acid in plasma of transplant recipients treated with mycophenolate mofetil. Brit. J. Pharmacol., 1999,126, 1075. 

Kittelmann, M., Rheinegger, U., Espigat, A., Oberer, L., Aichholz, R., Francotte, E. and Ghisalba O., Preparative enzymatic synthesis of the acylglucuronide of mycophenolic acid. Adv. Synth. Catal, 2003, 345, 825. 

Mycophenolate sodium (62 Myfortic ) Mycophenolic acid (61) Fatty acid antibiotic NP Microbial Immuno- suppression Inhibits inosine monophosphate dehydrogenase (IMPDH) activity 215-217, 532-560... 

Mycophenolate sodium (62 Myfortic Norvatis, 2003) is an immunosuppressant drug used to prevent rejection in organ transplantation. It is a selective, noncompetitive, reversible inhibitor of inosine monophosphate dehydrogenase (IMPDH), the rate-limiting enzyme in the de novo pathway of guanosine nucleotide synthesis. Thus, mycophenolic acid (61), originally... 

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