7- guanine, synthesis

YAMAZAKI-CLAUSEN (GEA) Guanine Synthesis Synthesis of guanine or of 9-substituted guanines using benzoylisothiocyanate. 

The mode of action has been a subject for research for a number of years. While it was originally thought that maleic hydrazide replaced uracil in the RNA sequence, it has been deterrnined that the molecule may be a pyrimidine or purine analogue and therefore base-pair formation is possible with uracil and thymine and there exists the probabiHty of base-pair formation with adenine however, if maleic hydrazide occurs in an in vivo system as the diketo species, then there remains the possibiHty of base-pairing with guanine (50). Whatever the mechanism, it is apparent that the inhibitory effects are the result of a shutdown of the de novo synthesis of protein. 

Guanine, 9-/3-D-ribofuranosyl-, 5, 536 Guanine, 6-thio-tautomerism, 5, 509 toxicity, 1, 141 Guanine, 8-trifluoromethyl-synthesis, 5, 574 Guanines, thio-synthesis, 5, 572 Guanosine arylation, 5, 538 dipole moment, 5, 522 free radical alkylation, 5, 543 hydrobromide... 

The steps involved in automated oligonucleotide synthesis illustrate the current use of protective groups in phosphate chemistry (Scheme 1). Oligonucleotide synthesis involves the protection and deprotection of the 5 -OH, the amino groups on adenine, guanine, and cytosine, and -OH groups on phosphorus. 

The synthesis and X-ray structure of a platinum(II) complex containing the well-known antiviral nucleoside acyclovir (9-(2-hydroxyethoxymethyl)guanine, acv) have been described.222 Treatment of acyclovir with [PtCl(DMSO)(en)]+ results in the formation of [Pt(en)(acv)2]2+ (74), whereby two acv molecules are coordinated to the platinum(II) center via their N-7 atoms. The related complex C7,y-[P tCl (NI13)2(acv)]+ (75) has also been reported.223... 

Bidentate sites may be available in DNA itself. In the binding of Hg2+ and Ag+ we surmise that the binding is to amino-groups of cytidine and adenine and possibly the N(7) of guanine as all these positions are accessable in DNA. The introduction of a more kinetically permanent group such at [Pt(NH3)2]2+ attached to two such groups, e.g. two amino groups could lead to the formation of an inter-strand cross-link and an inhibition of DNA synthesis (90). 

Fig. 4.5 The adenine synthesis can be varied to give other purine derivatives. Structures I-IX are those of I aminomalonitrile, II HCN tetramer, III aminoimidazole-carbonitrile, IV 4-aminoimidazole-5-carboxamide, V adenine, VI diaminopurine, VII xanthine, VIII guanine and IX hypo xanthine (Sanchez et al., 1966a)... 

The same problem, the stability of the nucleobases, was taken up by Levi and Miller (1998). They wanted to show that a synthesis of these compounds at high temperatures is unrealistic, and thus they took a critical look at the high temperature biogenesis theories, such as the formation of biomolecules at hydrothermal vents (see Sect. 7.2). The half-life of adenine and guanine at 373 K is about a year, that of uracil about 12 years and of the labile cytosine only 19 days. Such temperatures could have easily been reached when planetoids impacted the primeval ocean. 

The purine base guanine is also formed in concentrated solutions of ammonium cyanide, i.e., the same substance which became known from Or6 s adenine synthesis. Or6, as well as Stanley Miller, was involved in a new series of experiments (Levi et al., 1999). The yield of guanine is, however, 10 10 times lower than that of adenine surprisingly, the synthesis is just as effective at 253 K as at 353 K. Low temperatures seem conceivable in certain parts of Earth as well as on the Jovian moon Europa (see Sect. 3.1.5) or in the Murchison meteorite. 

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