Cyclic UMP

Nucleoside 2, 3 -cyclic phosphorothioates are prepared by reacting the 5 -acetylnucleoside with triimidazole phosphinsulfide followed by aqueous work-up and deblocking [17]. This procedure is illustrated in Fig. 5 for the exo- and endo-isomers of 2, 3 -cyclic uridine phosphorothioate, 2, 3 -cyclic UMPS, which were first synthesized by Eckstein and associates. The two could be separated because the endo- isomer is crystalline while the other is an oil. After repeated crystallization the pure endo- isomer was obtained and its crystal structure determined, giving its absolute configuration [18]. 

Fig. 24. Stereochemical inversion in the ribonuclease-catalyzed hydrolysis of emit/-2, 3 -cyclic UMPS in H O.

Figure 3. Ionizable groups and pKa values in 3 -UMP and 2 3 -cyclic UMP. Note that the second ionization which occurs in 3 -UMP at pH 5.9 is absent in 2, 3 -cyclic UMP. The unionizable OH groups on the ribose molecule are not shown...

In 1970, Eckstein and co-workers reported the first stereochemical study of an enzyme-catalyzed hydrolysis of a phosphate ester, the hydrolysis of the endo isomer of uridine 2, 3 -cyclic phosphorothioate (enrfo-cyclic UMPS) (72) by ribonuclease A (RNase A) 13). The hydrolysis of RNA catalyzed either by base or by RNase A proceeds by a two-step mechanism in which the 2 -hydroxyl group of a nucleotide unit within an RNA molecule acts as a nucleophile on the 3 -phosphodiester bond to displace the 5 -hydroxyl group of the neighboring nucleoside to form a 2, 3 -cyciic phosphate intermediate. RNase A then catalyzes the hydrolysis of this cyclic phosphate, mimicked by Eckstein s endo-cyclic UMPS, to yield the ultimate 3 -mononucleotide product. 

Figure 4. The effect of pH on the rate constants for the reactions of e ao with the mononucleotides of uracil. Note that 2 3f-cyclic UMP does not show a change in reactivity around pH6 as do 2, 3 -UMP (mixed) and 5f-UMP which become doubly ionized (UMP2 ) above this pH...

Azacytidine 2, 3, 5 -Tri-Ac, A-887 6-Azacytidine 2, 3, 5 -Tribenzoyl, A-887 6-Azacytidine, A-887 8-Azaguanosine 5 -Phosphate, A-888 6-Azathymidine 3, 5 -Diphosphate, A-891 6-Azathymidine 3 -Phosphate, A-891 6-Azathymidine 5 -Phosphate, A-891 8-Azidocyclic AMP, A-897 3 -Azido-3 -deoxy-5 -thymidylic acid, 9CI, Z-4 Benzyl 2-amino-4,6-0-benzylidene-2-deoxy-a-D-glucopyranoside 3-(dihydrogen phosphate), A-272 8-Bromocyclic AMP, B-53 8-Bromocyclic GMP, B-54 Bucladesine, INN, C-162 Bucladesine sodium, JAN, C-162 Coenzyme A, C-144 Coenzyme II, C-145 Coenzyme I, C-143 Cordycepin 5 -Triphosphate, C-152 Cyclic ADP-ribose, C-I6I Cyclic AMP A-Butanoyl, C-162 Cyclic AMP 2 -Deoxy, C-162 Cyclic AMP, C-162 Cyclic CMP, C-163 Cyclic GMP, C-164 Cyclic TMP, C-165 Cyclic UMP, C-166... 

When cyanoacetylene (5), which is produced when an electric discharge is passed through a mixture of methane and nitrogen, is dissolved in a phosphate buffer a stable enol-phosphate (6) is formed. Pyrophosphate is produced when neutral aqueous solutions of (6) and orthophosphate are heated, and the phosphorylation of UMP has been achieved. However, from a study of the rate of phosphorylation and a consideration of environmental factors, especially the likely phosphate concentration in oceans, it is suggested that (6) is not an important intermediate in prebiotic phosphorylation. The conversion of the 3 -phosphate of 0 2 -cyclocytidine (7) into 2, 3 -cyclic CMP under mild conditions in aqueous solution has... 

The phosphodiester substrates used for the model studies described herein are shown in Figure 8. ApA and 2, 3 -c-UMP represent several diribonucleotides and cyclic 2, 3 -cyclic ribonucleotides. 

These were differently affected by different procedures. For example, when the enzyme was activated at 55°, the increment in ki was slight, but k2 increased 3.5-fold. Similarly, in the presence of EDTA, fc, and k2 values decreased independently, suggesting that the sites for both activities were different. Center and Behai (5) found that with the P. mirabilis enzyme, cyclic 2, 3 -UMP competitively inhibited the hydrolysis of bis(p-nitrophenyl) phosphate. The Ki was 40 pAf very close to the Km for the cyclic nucleotide (Km, 75 yM) which indicated that the two compounds could serve as alternate substrates being hydrolyzed at the same active site. In contrast, 3 -AMP was a mixed inhibitor of cyclic 2, 3 -UMP and bis(p-nitrophenyl) phosphate hydrolysis. Adenosine was a mixed inhibitor of bis(p-nitrophenyl) phosphate hydrolysis but a competitive inhibitor of 3 -AMP hydrolysis. From such kinetic studies Center and Behai (5) suggested that two separate and adjacent sites A and B are involved in the hydrolysis of the diester and phos-phomonoester substrates. Site A serves as a binding site for hydrolysis of ribonucleoside 2, 3 -cyclic phosphates and together with site B catalyzes the hydrolysis of the diester bond. During this reaction 3 -... 

UMP becomes bound to site B which catalyzes the hydrolysis of the phosphomonoester bond. Adenosine and 3 -AMP by binding at site B could interfere with the breakdown of cyclic 2, 3 -UMP. Similarly, binding of bis (p-nitrophenyl) phosphate at site A could interfere with the breakdown of 3 -AMP. Cyclic 2, 3 -UMP and bis(p-nitrophenyl) phosphate compete for site A while adenosine competes with 3 -AMP for site B. Unemoto et al. (7) have examined the mutual inhibition of substrates and substrate analogs for the enzyme from halophilic V. alginolyticus. They also concluded that 3 -ribonucleotides and ribonucleo-side 2, 3 -cyclic phosphates are hydrolyzed at different sites. However, because of the nature of the mutual inhibition between 3 -AMP and bis(p-nitrophenyl) phosphate, they suggested that part of the site for the latter substrate overlaps with the 3 -nucleotidase site. At this time the precise mechanism of action of the enzyme is not settled, but clearly there are two active sites, one a 3 -nucleotidase site and a cyclic phosphate diesterase site. Anraku (18) has described this protein as a double-headed enzyme. 

Abbreviations used NAD+ = nicotinamide adenine dinucleotide NADH e reduced nicotinamide adenine dinucleotide NADP = nicotinamide adenine dinudeotide phosphate NAD PH reduced nicotinamide adenine dinucleotide phosphate NMN, NMN+ nicotinamide mononucleotide NMNH2 = reduced nicotinamide mononucleotide a-NAD a-nicotinamide adenine dinucleotide AMP = 5 -adenylic acid 3,5 -AMP adenosine 3, 5 -cycIic phosphate 3 ,5 -UMP = uridine 3, 5 -cyclic phosphate 3, 5 -CMP cytidine 3, 5-cyclic phosphate 3 f5 GMP = guanosine 3 5f-cyclic phosphate 3, 5 TMP thymidine 3, 5 -cyclic phosphate Dibutyryl-3, 5 -AMP = N6,02-dibutyryladenosine 3, 5 -cyclic phosphate 2, 3 -UMP = uridine 2 ,3 -cyclic monophosphate 2, 3 -CMP cytidine 2, 3 -cyclic monophosphate 2, 3 -AMP = adenosine 2, 3 -cyclic monophosphate 2 ,3 -GMP = guanosine 2 3 -cyclic monophosphate 2 -UMP = uridine 2 -phosphate -UMP uridine -phosphate 5 -UMP = uridine 5 phosphate Poly U polyuridylic acid ADP = adenosine 5 -diphosphate FAD = flavin adenine dinucleotide UpA, UpU, ApU and ApA x dinucleoside phosphates of uridine and/or adenine. c See original references for experimental conditions and additional data. 

Cyclo-UMP cyclic uridine 3, 5 -monophosphate. See Uridine phosphate ... 

Cytiic uridine 3,5 -monepho hate, cyeio-UMP, cUMP, M, 306.2, is a cyclic nucleotide, and like cyclic adenosine 3,5 -monophosphate (see Adenosine phosphates), it is involved in metabolic regulation. cUMP inhibits growth of some transplantable tumors. A specific cUMP-degiading enzyme is present in heart musele. 

When RNA is subjected to controlled alkaline hydrolysis eight nucleotides, two isomers each of AMP, GMP, cytosine monophosphate (CMP), and uridine monophosphate (UMP), are formed. These can be separated from one another on columns of anion exchange resins ISl), by paper chromatographic methods 1S2), and by fractional crystallization (iSS). The isomers are the 2 -phosphates ( a ) (XI) and 3 -phosphates ( b ) (XII) which arise from an intermediate cyclic 2, 3 -phosphate mononucleotide ester [Eq. (44)] (1S4-1S6). 

The thymidine oxyphosphorane 135 has been prepared by ester exchange, and underwent hydrolysis to give primarily the 5 -dialkyl phosphate. The cyclic analogue 136 of UMP has been synthesized for incorporation into antisense sequences to impart nuclease resistance. Its conformation was found to be similar to that of a nucleotide unit in A-type DNA duplexes. ... 

---