Orotic acid derivatives

Orotic acid derivatives belong to the group of pyrimidines. The pyrimidine ring is substituted by oxo, thio or amino groups in the positions 2 and 4. Several other groupings may be present (Fig. 209). 

A-Thiouracil 5-(M ethoxycarbonylmethyl)- 5-(Methoxycarbonyl-uracil methyl)-2-thiouraci I 

Secondary pyrimidine derivatives formed from orotic acid (Fig. 209) occur in microorganisms, plants and animals. 

D 16 Secondary Products Built from l-Aspartic Acid 

1 Aspartate carbamyltransferase 2 dihydroorotase 3 orotate reductase 4 orotate phosphoribosyl-transferase 5 orotidine-5 -phosphate decarboxylase 6 cytidylate kinase, nucleotide diphosphate kinase 7 cytidine triphosphate synthetase 8 nucleoside monophosphate kinase, ribonucleoside diphosphate reductase, phosphatase 9 thymidylate synthase 

---

The treatment of hydantoin derivatives (1293) with alkali metal hydroxide in boiling aqueous ethanol for 1 -2 hr gave orotic acid derivatives (1294) in good yields (82EUP52341). 

Calculations have so far answered some questions related to the decarboxylation of orotic acid derivatives in different media, but these same computational studies have also opened up many additional areas of controversy. 

G13 Golovinsky, E., Kaneti, J., Yukhnovsky, I. and Genchev, D. A study of some orotic acid derivatives and analogues by... 

G17 Golovinsky, E., Markov, K. and Maneva, L. Effect of some orotic acid derivatives and analogs on the growth of microorganisms. Izv. Inst. Biokhim. Bulg. Akad. Nauk., 4, 17-26 (1973) (Bulg.)... 

K3 Kaneti, J., Golovinsky, E., Yukhnovsky, I. and Genchev, D. A study of some orotic acid derivatives and analogues by Huckel s method of molecular orbitals. I. A theoretical study of the active site of orotidine-5 -phosphate pyrophos-phorylase. J. Theor. Biol., 26, 19-27 (1970)... 

L-Aspartic acid derivatives L-Asparagine (D 16) Secondary orotic acid derivatives (D 16.1) Trigonelline (D 16.2)... 

Complementary triple hydrogen-bond formation involving transition metal complexes has been little studied. Mingos et al. [68] have investigated the cocrystallisation of platinum(II) complexes of the uracil derivative orotic acid (2,6-dioxo-l,2,3,6-tetrahydropyrimidine-4-carboxylic acid), which generally coordinates as the dianion, and 2,6-diaminopyridine (2,6-dap), in which complementary A-D-A---D-A-D triple hydrogen bonds are formed between the orotate... 

These three compounds exert many similar effects in nucleotide metabolism of chicks and rats [167]. They cause an increase of the liver RNA content and of the nucleotide content of the acid-soluble fraction in chicks [168], as well as an increase in rate of turnover of these polynucleotide structures [169,170]. Further experiments in chicks indicate that orotic acid, vitamin B12 and methionine exert a certain action on the activity of liver deoxyribonuclease, but have no effect on ribonuclease. Their effect is believed to be on the biosynthetic process rather than on catabolism [171]. Both orotic acid and vitamin Bu increase the levels of dihydrofolate reductase (EC 1.5.1.4), formyltetrahydrofolate synthetase and serine hydroxymethyl transferase in the chicken liver when added in diet. It is believed that orotic acid may act directly on the enzymes involved in the synthesis and interconversion of one-carbon folic acid derivatives [172]. The protein incorporation of serine, but not of leucine or methionine, is increased in the presence of either orotic acid or vitamin B12 [173]. In addition, these two compounds also exert a similar effect on the increased formate incorporation into the RNA of liver cell fractions in chicks [174—176]. It is therefore postulated that there may be a common role of orotic acid and vitamin Bj2 at the level of the transcription process in m-RNA biosynthesis [174—176]. 

Some sulphur-containing derivatives, such as 2-hydroxy-4-mercapto [36a] (X), 4-hydroxy-2-methylthio-[36a] (XI), 2-hydroxy-4-methylthio-[36a] (XII), and 2,4-bis(methylthio)-6-pyrimidinecarboxylic acid [36a] (XIII), can cause more than 50 per cent inhibition of orotic acid metabolism by cell-free extracts from mouse liver or L5178Y leukaemia cells at concentrations less than 2 x ICT M[207]. 5-Diazo-orotic acid (IX) has recently been found to possess good inhibitory activity against leukaemia L-1210 in mice [212]. 

Ethyl 2-ethylthio-4-chloro-5-pyrimidinecarboxylate (XXIIa), as well as the corresponding4-hydroxy-(XXIIb) and 4-amino-(XXIIIa) derivatives, possess-anti-cytogenic activity on Neurospora crassa [223, 224]. Compounds (XXIIIa, b and c) were found to inhibit the conversion of orotic acid to the uridine nucleotides [202]. Ethyl 2-methylthio-4-(halo-substituted anilino)-5-pyrimidinecarboxylates (XXIV), particularly the o-bromo- and the o-chloro- derivatives, substantially inhibit the growth of five experimental mouse tumours (Krebs-2 ascites carcinoma, Ehrlich carcinoma clone 2, leukaemia L-1210, carcinoma 755 and lymphocytic neoplasm P-288) [225]. Compounds of this type are usually prepared by the base catalysed condensation of ethoxymethylenemalonic esters or related derivatives with urea, thiourea, guanidine, or substituted amidine-type analogues [212, 225-237]. 

Orotic acid readily forms dimers even when irradiated in liquid medium [582, 583]. 5-Bromouracil (5-BrU) in DNA is dehalogenated, rather than forming cyclobutane-type dimers. Such DNA derivatives are more sensitive to ultraviolet irradiation than normal DNAs [584-594], Irradiation of 5-bromo-uracil and derivatives in aqueous medium produces 5,5 -diuracil [590, 591]. However, derivatives such as 3-sbutyl-5-bromo-6-methyluracil have been reported to yield cyclobutane dimers either by irradiation of frozen aqueous solutions, or by catalysis with free radical initiators, such as aluminium chloride, ferric chloride, peroxides or azonitriles [595]. 5-Hydroxymethyluracil is reported to dimerize very slowly in frozen water at 2537 A [596]. The fundamental research in the photochemistry of the nucleic acids, the monomeric bases, and their analogues has stimulated new experiments in certain micro-organisms and approaches in such diverse fields as template coding and genetic recombination [597-616]. 

The most important pyrimidine derivatives are those upon which biological organisms depend. Cytosine 1018 and uracil 1019 are found in ribonucleic acid (RNA) in the form of their ribonucleotides, cytidine 1020 and uridine 1021, while in deoxyribonucleic acid (DNA), cytosine and thymine 1022 are found in the form of their 2 -deoxyribonucleotides, 2 -deoxycytidine 1023 and thymidine 1024. 5-Methylcytosine 1025 is also found to a small extent (c. 5%) in human DNA in the form of its 2 -deoxyriboside 1026, and 5-(hydroxymethyl)cytosine-2 -deoxyriboside 1027 has also been detected in smaller amounts <2005CBI1>. Many variants of cytosine and uracil can be found in RNA including orotic acid 1028 in the form of its ribonucleotide orotidine 1029. Other pyrimidine derivatives to have been isolated from various biological sources include 2 -deoxyuridine 1030, alloxan 1031, and toxopyrimidine (pyramine) 1032 (Figure 2). 

Hayon447 to absorb in this UV region. Similar measurements have been made for a number derivatives of uracil (5,6-dihydro, 1-, 3-, and 6-methyl, 1,3-dimethyl-, and 5-aminouracil, orotic acid, barbituric and isobarbituric acids also see similar measurements448 on 5-bromouracil and its iV-methyl derivatives), thymine itself and its derivatives (5,6-dihydro, 2-methylthymine). In the case of cytosine, Hayon447 has very tentatively suggested that species 47 and 48 are obtained on pulse radiolysis of the solution at pH 5.5, and 49 at pH 13.3. 

Although it is reasonable to assume from the enzymic studies cited162 that orotidine possesses the /3 configuration at the anomeric center, unequivocal determination of this feature is to be desired. Of interest is the fact that 1,3-dimethylorotic acid,119 3-methylorotic acid,119 163 and orotic acid itself are decarboxylated to the corresponding uracil derivatives at elevated temperatures. If orotidine could be decarboxylated in some similar fashion to uridine, the complete structure of XXXII would be established. 

The major bases found in nucleic acids are adenine and guanine (purines) and uracil, cytosine, and thymine (pyrimidines). Thymine is found primarily in DNA, uracil in RNA, and the others in both DNA and RNA. Their structures, along with their chemical parent compounds, purine and pyrimidine, are shown in Figure 10.1, which also indicates other biologically important purines that are not components of nucleic acids. Hypoxanthine, orotic acid, and xanthine are biosynthetic and/or degradation intermediates of purine and pyrimidine bases, whereas xanthine derivatives—caffeine, theophylline, and theobromine—are alkaloids from plant sources. Caffeine is a component of coffee beans and tea, and its effects on metabolism are mentioned in Chapter 16. Theophylline is found in tea and is used therapeutically in asthma, because it is a smooth muscle relaxant. Theobromine is found in chocolate. It is a diuretic, heart stimulant, and vasodilator. 

These three main studies of the gas phase behavior of orotate derivatives show that the 4-protonation pathway is always favored over the 2-protonation pathway. When the barriers are calculated relative to a common reference point of orotic acid, as was done in the Singleton-Beak-Lee study, the 4-protonation pathway is favored by a considerable amount, due mostly to the higher basicity of the 4-oxygen over the 2-oxygen in orotate. Still, the 4-protonation pathway also seems to be favored intrinsically, as evidenced by the consistently lower barriers computed for decarboxylation of the 4-protonated zwitterion 6, regardless of the Nl-R group. 

Of 2,4-dialkoxypyrimidines, only 2,4di-tert-butoxy pyrimidine19 and 5-nitro-2,4-dimethoxypyrimidine20 failed to react in the normal Hilbert-Johnson fashion, and anomalous O-2-glycosyl derivatives have been obtained21 with a 2,4-dialkoxypyrimidine substituted in position 6, namely, with 2,4-diethoxy-6-meth3dpyrimidine anomeric 2-tetra-0-acetyl-D-glucopyranosyloxy-4-ethoxy-6-methylpyrimidines (18) resulted. Unsuccessful attempts to synthesize an X-l-ribo-furanosyl derivative of orotic acid (uracil-6 carboxylic acid) have been reported.22... 

Brequinar (DUP 785, NSC 368390) is a quinoline carboxylic acid derivative that inhibits pyrimidine synthesis by inhibiting dihydro-orotate dehydrogenase. It was originally developed as an anticancer drug, but has also been investigated for its immunosuppressant activity after transplantation. Some data suggest that that the immunosuppressant activity of brequinar may be partly due to inhibition of tyrosine phosphorylation in lymphocytes (1). 

Fluorinated biologically active pyrimidines and purines 80YGK1119. Guanidine derivatives of purine from marine natural products 81Mn4. Orotic acid, physiological activity of 85PHA377. 

Pyrimido[5.4-r/]pyrimidines 5 and 6 are readily prepared by the condensation of 5-amino-2,6-dihydroxypyrimidine-4-carboxylic acid ( orotic acid ) with formamidc or urea. Reaction of the starting pyrimidine with formamide gives pyrimido[5,4-c/]pyrimidine-2,4,8-triol (5), which can also be prepared from ethyl 5-aminoorotate in 72% yield. In this case, the 5-amino group is first converted into the (ethoxymethylene)amino derivative and then treated with ammonia.207 The corresponding tetrol 6 results from reaction of the starting pyrimidine with urea.152,203... 

Uracil 22, thymine 23, cytosine 24, barbituric acid 25 and orotic acid 26 are important pyrimidine derivatives. 

---