Inactivation of S-adenosyl-L-homocysteine hydrolase by amide and ester derivatives of adenosine-5'-carboxylic acid

Synthesis of novel peptidyl adenosine antibiotic analogs

A small library of peptidyl adenosine antibiotic analogs was synthesized, under the Pilot Scale Library Program of the NIH Roadmap initiative, from 2',3'-O-isoproylideneadenosine-5'-carboxylic acid 2 in excellent yield. The coupling of the amino terminus of L-2-aminophenylbutyric methyl ester to a free 5'-carboxylic acid moiety of 2 followed by sodium hydroxide treatment led to carboxylic acid analog 4. Hydrolysis of this latter gave unprotected nucleoside analog 5. Intermediate 4 served as the precursor for the preparation of novel peptidyl adenosine analogs 6-18 in good yields and high purity through peptide coupling reactions to diverse amine derivatives. No marked anticancer and antimalaria activity was noted on preliminary cellular testing; however these analogs should be useful candidates for other types of biological activity.

Parallel solution-phase synthesis and general biological activity of a uridine antibiotic analog library

A small library of ninety four uridine antibiotic analogs was synthesized, under the Pilot Scale Library (PSL) Program of the NIH Roadmap initiative, from amine 2 and carboxylic acids 33 and 77 in solution-phase fashion. Diverse aldehyde, sulfonyl chloride, and carboxylic acid reactant sets were condensed to 2, leading after acid-mediated hydrolysis, to the targeted compounds 3–32 in good yields and high purity. Similarly, treatment of 33 with diverse amines and sulfonamides gave 34–75. The coupling of the amino terminus of d-phenylalanine methyl ester to the free 5′-carboxylic acid moiety of 33 followed by sodium hydroxide treatment led to carboxylic acid analog 77. Hydrolysis of this material gave analog 78. The intermediate 77 served as the precursor for the preparation of novel dipeptidyl uridine analogs 79–99 through peptide coupling reactions to diverse amine reactants. None of the described compounds show significant anticancer or antimalarial acivity. A number of samples exhibited a variety of promising inhibitory, agonist, antagonist, or activator properties with enzymes and receptors in primary screens supplied and reported through the NIH MLPCN program.

Inactivation of S-adenosylhomocysteine hydrolase with haloethyl and dihalocyclopropyl esters derived from homoadenosine-6′-carboxylic acid

In a search for new inhibitors that exploit 5'-6' 'hydrolytic activity' of AdoHcy hydrolase, a new series of haloethyl and dihalocyclopropyl esters 2-3 were designed and their interaction with the enzyme studied. Incubation of the enzyme with 2-3 resulted in time- and concentration-dependent inactivation of AdoHcy hydrolase as well as almost total depletion of its NAD(+) content. Further results indicated that the 'oxidative' but not the 'hydrolytic' activity was involved in the inactivation process.

Interactions of (-)-ilimaquinone with methylation enzymes: implications for vesicular-mediated secretion

BACKGROUND

The marine sponge metabolite (-)-ilimaquinone has antimicrobial, anti-HIV, anti-inflammatory and antimitotic activities, inhibits the cytotoxicity of ricin and diptheria toxin, and selectively fragments the Golgi apparatus. The range of activities demonstrated by this natural product provides a unique opportunity for studying these cellular processes.

RESULTS

Affinity chromatography experiments show that (-)-ilimaquinone interacts with enzymes of the activated methyl cycle: S-adenosylmethionine synthetase, S-adenosylhomocysteinase and methyl transferases. Known inhibitors of these enzymes were found to block vesicle-mediated secretion in a manner similar to (-)-ilimaquinone. Moreover, the antisecretory effects of (-)-ilimaquinone and inhibitors of methylation chemistry, but not brefeldin A, could be reversed in the presence of the cellular methylating agent S-adenosylmethionine. Of the enzymes examined in the activated methyl cycle, S-adenosylhomocysteinase was specifically inhibited by (-)-ilimaquinone. Consistent with these observations, (-)-ilimaquinone was shown to obstruct new methylation events in adrenocorticotrophic hormone (ACTH)-secreting pituitary cells.

CONCLUSIONS

(-)-ilimaquinone inhibits cellular methylations through its interactions with S-adenosylhomocysteinase. Furthermore, these studies indicate that the inhibition of secretion by ilimaquinone is the result of the natural product's antimethylation activity. It is likely that the ability to fragment the Golgi apparatus, as well as other activities, are also related to ilimaquinone's influence on methylation chemistry.

The mechanism of inactivation of S-adenosylhomocysteine hydrolase by fluorinated analogs of 5'-methylthioadenosine

5'-Deoxy-5'-difluoromethylthioadenosine (DFMTA) 1a and 5'-deoxy-5'-trifluoromethyl-thioadenosine (TFMTA) 1b are inhibitors of beef liver S-adenosyl-L-homocysteine hydrolase. DFMTA and TFMTA are time-dependent and irreversible inhibitors of the enzyme. Both 1a and 1b are oxidized by E-NAD+ to produce E-NADH and fluoride anion is formed in the inactivation reaction (2.2 mol of fluoride/mole of enzyme subunit and 3.1 fluoride/mole of enzyme subunit from DFMTA and TFMTA respectively). Using [8-3H]-1a or [8-3H]-1b no trace of labelled adenosine was detected during the inactivation reaction but adenine was formed. The mechanism of inhibition of S-adenosyl-L-homocysteine hydrolase by these two fluorinated nucleosides is discussed.

Photoaffinity study of the cellular interactions of ilimaquinone

The marine sponge metabolite ilimaquinone (1) displays a broad range of biological activities. To better understand the effects of this natural product, a photoaffinity analogue was synthesized and used to probe the cellular interactions of ilimaquinone. Irradiation of photoaffinity probe 5 with liver cytosol in the presence and absence of excess competitive inhibitor 2 suggests that S-adenosylhomocysteinase is an important intracellular target of ilimaquinone.