Cyclization reactions of guanidino groups

Guanidino compounds can be readily cyclized by reaction with malondialdehyde, either as such or in the form of its diethyl acetal, 1,1,3,3-tetraethoxypropane, giving substituted pyrimidines, which may have improved chromatographic properties increased detectability (UV absorption after TLC) and potentially also increased volatility for analysis by GC [93,94], 

A solution of arginine (1 mmol) and 1,1,3,3-tetraethoxypropane (10% molar excess) in 8 ml of 12 M HCl is allowed to stand for 3h at room temperature, then evaporated to dryness on a rotary evaporator. The solution may be analysed by TLC at this stage, or further purified on a column of Dowex 50-X8 by elution with a pyridine/acetic acid gradient. Elution is monitored by UV absorption at 315 nm. Gas chromatographic analysis may be carried out after further derivatization of the ornithine side chain [94], 

The guanidino-compound, either a drug such as 3-hydroxyguanfacine, debrisoquine or guanadrel [95-98] or a naturally occurring guanidine such as d-guanidino-valeric acid [99], is extracted from urine or plasma (2 ml), and the extract is evaporated to dryness. To the residue is added a 10% solution of hexafluoroacetylacetone in methanol (200 fi ) and the mixture is heated for an hour or two at 100 °C. The solution is evaporated to dryness, and the product may be analysed by TLC, or further 

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