A. R. Simonian

The Use of Novel C-Methylated Spermidine Derivatives To Investigate the Regulation of Polyamine Metabolism

The polyamines are organic polycations present at millimolar concentrations in eukaryotic cells where they participate in the regulation of vital cellular functions including proliferation and differentiation. Biological evaluation of rationally designed polyamine analogs is one of the cornerstones of polyamine research. Here we have synthesized and characterized novel C-methylated spermidine analogs, that is, 2-methylspermidine, 3-methylspermidine, and 8-methylspermidine. 3-Methylspermidine was found to be metabolically stable in DU145 cells, while 8-methylspermidine was a substrate for spermidine/spermine N(1)-acetyltransferase (SSAT) and 2-methylspermidine was a substrate for both SSAT and acetylpolyamine oxidase. All the analogs induced the splicing of the productive mRNA splice variant of SSAT, overcame growth arrest induced by 72-h treatment with ornithine decarboxylase (ODC) inhibitor α-difluoromethylornithine, and were transported via the polyamine transporter. Surprisingly, 2-methylspermidine was a weak downregulator of ODC activity in DU145 cells. Our data demonstrates that it is possible to radically alter the biochemical properties of a polyamine analog by changing the position of the methyl group.

Novel convenient synthesis of biologically active esters of hydroxylamine

Alkylation of ethyl N-hydroxyacetimidate with readily available methanesulfonates of functionally substituted alcohols and subsequent deprotection of aminooxy group is a novel and convenient method to prepare functionally substituted esters of hydroxylamine with high overall yield. This approach is a good alternative to well-known reaction of N-hydroxyphthalimide with alcohols under the Mitsunobu conditions. The properties of ethoxyethylidene protection of aminooxy group on the contrary to that of N-alkoxyphthalimide group allow to perform a wide spectra of the transformations in the radical of N-protected hydroxylamine derivatives. This is essential for synthetic strategies consisting in the introduction of N-protected aminooxy group at one of the first steps of synthesis and subsequent transformations of the radical.The inhibitory effect of one of the newly synthesized compound, 1-guanidinooxy-3-aminopropane (GAPA), was compared with that of well-known inhibitors of ornithine decarboxylase namely, α-difluoromethylornithine (DFMO) and 1-aminooxy-3-aminopropane (APA) on Leishmania donovani, a protozoan parasite that causes visceral leishmaniasis. GAPA, on the contrary with APA and DFMO, in micromolar concentrations, inhibited the growth of both amastigotes and promastigotes of sodium antimony gluconate-resistant forms of L. donovani.

Methylated analogs of spermine and spermidine as tools to investigate cellular functions of polyamines and enzymes of their metabolism

Biogenic amines spermine (Spm) and spermidine (Spd) are essential for cell growth. Polyamine analogs are widely used to investigate the enzymes of polyamine metabolism and the functions of spermine and spermidine in vitro and in vivo. It was demonstrated recently that α-methylated derivatives of Spm and Spd are able to fulfill the key cellular functions of polyamines, moreover, in some cases, the effects of (R) and (S) isomers were actually different. Using these α-methylated analogs of Spm and Spd, it turned possible to prevent the development of acute pancreatitis in SSAT-transgenic rats with controllable expression of the Spm/Spd N1-acetyltransferase gene. The analogs made it possible to reveal dormant stereospecificity of polyamine oxidase, Spm oxidase, and deoxyhypusine synthase. An original approach was suggested to regulate the stereospecificity of polyamine oxidase. Depletion of the intracellular polyamine pool was found to have both hypusine-related consequences and consequences unrelated to posttranslational modification of the eukaryotic translation initiation factor eIF5A. Possible applications of a new family of C-methylated polyamine analogs for the investigation and regulation of polyamine metabolism in vitro and in vivo are discussed.

Biogenic Polyamines Spermine and Spermidine Activate RNA Polymerase and Inhibit RNA Helicase of Hepatitis C Virus

Influence of the biogenic polyamines spermine, spermidine, and putrescine as well as their derivatives on the replication enzymes of hepatitis C virus (HCV) was investigated. It was found that spermine and spermidine activate HCV RNA-dependent RNA polymerase (NS5B protein). This effect was not caused by the stabilization of the enzyme or by competition with template-primer complex, but rather it was due to achievement of true maximum velocity Vmax. Natural polyamines and their derivatives effectively inhibited the helicase reaction catalyzed by another enzyme of HCV replication — helicase/NTPase (NS3 protein). However, these compounds affected neither the NTPase reaction nor its activation by polynucleotides. Activation of the HCV RNA polymerase and inhibition of the viral helicase were shown at physiological concentrations of the polyamines. These data suggest that biogenic polyamines may cause differently directed effects on the replication of the HCV genome in an infected cell.

Methylated Polyamines as Research Tools

Earlier unknown racemic β-methylspermidine (β-MeSpd) and γ-methylspermidine (γ-MeSpd) were -synthesized starting from crotononitrile or methacrylonitrile and putrescine. Lithium aluminum hydride reduction of the intermediate di-Boc-nitriles resulted in corresponding di-Boc-amines, which after deprotection gave target β- and γ-MeSpds. To prepare α-MeSpd, the starting compound, 3-amino-1-butanol, was converted into N-Cbz-3-amino-1-butyl methanesulfonate, which alkylated putrescine to give (after deprotection of amino group) the required α-MeSpd. Novel β- and γ-MeSpds in combination with earlier α-MeSpd are useful tools for studying enzymology and cell biology of polyamines.

Novel metabolically stable and functionally active mimetic of spermidine

Earlier unknown 1,8-diamino-3-methyl-4-azanonane (γ-MeSpd) was synthesized. The analogue was a substrate of neither spermine/spermidine N1-acetyltransferase nor spermine synthase, but was capable to support the growth of DU145 cells having depleted polyamine pools. Such a combination of γ-MeSpd properties discloses novel opportunities to study cellular functions of catabolically unstable and easily interconvertible spermine and spermidine.

Leishmania donovani: structural insignt in the recognition of C-methylated analogues of spermidine as natural polyamines

The ability of α-, ν-, γ- and ω-methylated spermidine analogues to restore the growth of L. donovani promastigotes that were depleted of putrescine and spermidine was investigated. Only β-methylated spermidine, like natural spermidine, was capable of restoring the growth of L. donovani, while the remaining three analogues turned out to be inactive. α-Methylated spermidine is a functionally active spermidine surrogate both in vivo and in vitro, hence this analogue may be considered as an antidote in the host-parasite system, especially in the cases where inhibitors of polyamine biosynthesis are used for the therapy of leishmaniasis.

Novel hydroxylamine-containing analogues of 1-guanidino-7-aminoheptane (GC7), an effective inhibitor of deoxyhypusine synthase

Earlier unknown hydroxylamine-containing analogues of 1-guanidino-7-aminohepane (GC7) containing the free aminooxy group (1-aminooxy-6-guanidinohexane), bis-guanyl derivatives of 1-aminooxy-6-aminohexane, and 1-aminooxy-5-aminopentane, and mono-guanidinooxy analogue (1-guanidinooxy-6-aminohexane) were synthesized in high overall yields from commercially available 5-(Boc-amino)1-pentanol and 6-(Boc-amino)-1-hexanol. It was demonstrated that 1,3-di-Boc-2-(trifluoromethylsulfonyl)guanidine is able to specifically amidinate the amino group in the presence of the free aminooxy group. The application of newly synthesized GC7 analogues for the investigation of the peculiarities of their interaction with the active site of deoxyhypusine synthase was discussed.

Synthesis of 2,11-bis(methylidene)spermine, a new inhibitor of spermine oxidase

Earlier unknown 1,12-diamino-2,11-bis(methylidene)-4,9-diazadodecane, which may be considered as an enzyme-activated inhibitor of spermine oxidase, was synthesized in 6 steps starting from 2-chloromethyl-3-chloropropene-1 in a high yield. Application of newly synthesized spermine analogue for the inhibition of spermine oxidase was discussed.