The synthesis of 6-azidomethyl-5,6,7,8-tetrahydropterin (6-AzmH 4 Ptr) (9) starting from 2,4-diamino- 6-hydroxymethylpteridine (1) is described. A special protecting group strategy had to be applied to perform the structural modifications. The introduction of the azido function was achieved by a Mitsunobu reaction converting the N 2 - N ,N -dimethylaminomethylen-6 -hydroxymethyl-5-pivaloyl-5,6,7 ,8-tetrahydropterin (7) with diphenylphosphoryl azide into the corresponding 6-azidomethyl derivative (8). The newly synthesized compounds have been characterized by elemental analyses, UV, IR and 1 H-NMR spectra. The photolysis of 6-AzmH 4 Ptr (9) and its inactivation effect upon aromatic amino acid mono oxygenases has been studied
Reaction of 2-amino-4-butoxypteridine (1) with alkyl- or phenylmagnesium bromide followed by protonative and oxidative work-up with a solution of iodine in acetic acid gives 7 -alkyl- or 7 -phenylpteridines (2 ). Regioselective oxidation of 1 to 2-amino-4-butoxypteridine 8-oxide (3) by hydrogen peroxide proceeds in trifluoroacetic acid, and reaction of 3 with Grignard reagent or an organolithium compound affords 2 together with its 8-oxide 4. The products (2 and 4) are easily derived to 7-substituted 2-amino-4- hydroxypteridines. The mechanism of the regioselectivity can be explained based on electron density and molecular orbitals (MO) which are obtained by calculation on the methoxy analogs of 1 and 3.
Breast milk has been found to contain high levels of biopterin compounds, whose physiological roles have attracted attention through newly discovered functions, particularly. as a cofactor for biosynthesis of nitric oxide. the biopterin level in serum and the volume of urinary excreted biopterin in neonatals. 1) The concentration of total biopterin in breast milk increased daily to a maximum value from the 7- 11 th day postpartum. then decreased to as low as one third of the peak value. 2) The daily ingestion of biopterin also increased. After a peak during the 7-9 th days. it then reduced to a constant level after 1 month. 3) The serum biopterin level on the 4 th day after birth showed a relatively constant value and had no correlation with the ingested amount of biopterin on the 3rd day. 4) No correlation existed between the level of urinary biopterin excreted and the ingested amount of breast milk. We concluded that orally ingested, concentrated biopterin may have no influence no the serum level of biopterin and urinary excreted biopterin .
We previously reported that intracerebroventricular administration of 6R-L-erythro-5,6,7,8-tetrahy drobiopterin (6R-BJL), a cofactor for aromatic amino acid hydroxylases and nitric oxide synthase, induces an increase in DOPA levels (as an index of DA biosynthesis) and in levels of DA metabolites (as an index of DA release) in the rat brain: the increase in DOPA levels was larger than that of DA metabolites, indicating that 6R-BH 4 enhances DA release. In the present study, we examined the effects of 6R-BH 4 on DA release in vivo from the striatum of male Wistar rats and its mechanism of action using brain microdialysis. When various concentrations of 6R-BJL, 6S-BH 4 (a diastereoisomer of 6R-BH 4 ) or 6-methyltetrahydropterin (6-MPH 4 ) were added to the perfusion fluid of microdialysis probes, DA levels collected in dialysates increased in a concentration-dependent manner: the 6R-BJL-induced increase was far greater than the increase induced by 6S-BH 4 or 6-MPH 4 . Biopterin had little effect on the DA levels. After i.p. injection of 250 mg/kg of α-methyl-p-tyrosine (α-MT; an inhibitor of tyrosine hydroxylase), most of the 6R BH 4 - induced increase persisted but the increase induced by 6S-BJL or 6-MPH4 was abolished. The 6R-BH 4 -induced increase in DA levels in dialysates was abolished after addition of tetrodotoxin (50 μM) to the perfusion fluid, but it persisted after i.p. injection of 100 mg/kg of nomifensine which completely inhibited DA reuptake. The increase in DA levels also persisted after administration of nitric oxide synthase inhibitors. The 6R-BJL-induced increase in DA levels was inhibited by co-administration of 6S-BJL or 6-MPH 4 . Administration of sepiapterin (an immediate precursor of 6R-BJL) increased tissue levels of reduced biopterin (mainly consisting of 6R-BH 4 ) but not its extracellular levels monitored by brain microdialysis, indicating that it selectively increases the intracellular 6R-BJL levels. In contrast, administration of 6R-BH 4 increased both tissue levels of reduced biopterin and its extracellular levels, indicating that it increases both the intra- and extra-cellular 6R-BH 4 leveles. DA levels in dialysates was elevated following administration of sepiaterin (an immediate precursor of 6R-BH 4 ), but the elevation was abolished after pretreatment with α-MT. Furthermore, 6R-BH 4 increased firing rates of neurons in the dorsal motor nucleus of vagus monitored by a slice patch method. These results suggest that 6R-BH 4 has a DA releasing action independent of its cofactor for tyrosine hydroxylase and nitric oxide synthase, which is mediated by a specific recognition site for 6R-BH 4 on DA neurons or related cells.
The in vitro antioxidative activity of neopterin and its in vivo potency to suppress gastric ischemia were investigated. The scavenging activity of the reduced form of neopterin, 5,6,7,8-tetrahydroneopterin (NPH4), against superoxide anion radicals, showed an extremely high superoxide anion radical scavenging activity in two assay systems, i.e., hypoxanthine/xanthine oxidase (HPX/XOD) and rat macrophage/ phorbol myristate acetate (Mø/PMA) radical-generating systems. The antioxidative activities against both super oxideanion and hydroxyl radicals were confirmed by spin trapping-ESR spectrometry. In contrast, the oxidized form of neopterin (NP) did not show any activity in the HPX/XOD system, but was effective in the Mø/PMA system. These data suggest that NPH4 directly scavenges superoxide anion radicals, while NP suppresses the superoxide anion generation in macrophages through its inhibitory effect on the membrane NADPH-oxidase. Furthermore, NPH4 and NP effectively suppressed the formation of gastric injury induced by ischemia and reperfusion. These results suggest that neopterin play an important role as an endogenous antioxidant.
The levels of neopterin, biopterin and the neopterin/biopterin ratio (NIB) were measured in urine samples taken from normal young and elderly control subjects, exceptionally healthy elderly control subjects classified according to the 'Senieur' protocol and patients with Down`s syndrome (DS ) or Alzheimer's disease (AD). The NIB ratio was approximately unity in the control groups with the exception of the normal elderly controls. The levels of neopterin and biopterin declined with age in the exceptionally healthy 'Senieur' control group. The NIB ratio was elevated in young and old DS patients as a result of a significant increase in neopterin. Neopterin levels were significantly elevated in AD patients compared with the healthy elderly controls, but this did not result in a significant increase in the NIB ratio in these patients. The NIB ratio increased with age in AD patients as a result of a decline in biopterin. These results suggested that there is a cellular immune response in DS and AD patients which in DS, may precede the formation of β-amyloid deposits in the brain. In addition, there may be a deficiency in tetrahydrobiopterin biosynthesis in AD which becomes more marked with age.
Neopterin, a compound derived from GTP, is a percursor molecule of biopterin and is an essential cofactor in neurotransmitter synthesis. It has recently reported that in vivo as well as in vitro immune responses are accompaniced by an increased release of neopterin and that this phenomenon can be used for the biochemical monitoring of diseases accompanied by hyperimmune stimulation. This article describes the immune response-associated neopterin release in the brain, and the possible involvement of microglia.
