RESEARCH
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Emphasis @n Purines Importance of purines in rnefaboiic processes stimulates research on synthesis of new derivatives Activity of various kinds—antitumor, trypanocidal, fungicidal, bactericidal—have all been found among the d e antagonists—of the p u -
R. U. Lemieux (left) a n d R . K. Kullnig of University of Ottawa look for such fine points of structure as t h e shape of molecules on the strip c h a r t of a nuclear magnetic resonance apparatus spectrometer. T h e Canadian scientists have used nmr of the proton to find such detailed points
Shapely Protons Nuclear magnetic resonance of the proton now tells fine points of structure Nuclear m a g [ netic resonance of the proton can now tell the difference between I axial a n d equatorial hydrogens in a molecule, say R. U . Lemieux and R. K. Kullnig of the University of O t t a w a . This ability to detect such fine points of structure as t h e conformation or shape of molecules opens the way t o determining t h e chemical and biological properties of a whole h o s t of organic materials. Here's h o w it works. A c o m p o u n d is placed i n t h e instrument's magnetic field, Kullnig told t h e Division of Carbohydrate Chemistry. T h e n b y sweeping the field, signals for hydrogen i n different electronic surroundings within t h e molecule a r e received. These i n t u r n are recorded on a strip chart as a permanent record for interpretation. ( I f so desired, recordings can b e p i c k e d up on an oscillograph.) For one compound the Canadians worked with, meso-inositol hexaacetate, t h e chart shows four distinct peaks, meaning there a r e four types of protons within t h e molecule. T w o b a n d s appeared a t 142 and 184 cycles per second (chart scale). Some distance apart a n o t h e r pair showed u p at 8 and
0 c.p.s. By measuring the distance between peaks, ratios of 1 t o 5 w e r e found for the higher frequencey, 3 t o 15 for t h e lower one. This information was then compared with known data on mgso-inositol hexaacetate from chemical characterization analyses. F o r example, t h e c o m p o u n d has six free hydrogens a n d 18 h y d r o gens in the acetoxy groups. But, what proton n m r tells, a n d other analytical tools d o not, is t h a t for t h e 1 to 5 ratio there are five axial hydrogen atoms, with t h e remaining one an equatorial hydrogen. F o r t h e 3 to 15 acetoxy-group ratio, t h e r e a r e three hydrogens in t h e axial acetoxy group, 15 hydrogens in t h e equatorial acetoxy groups. Hence, s h a p e of the inositol molecule, a d d s Kullnig, is known. N m r is t h e only m e t h o d which distinguishes axial a n d equatorial hydrogens. S o far Kullnig's work h a s been w i t h carbohydrates such as t h e fully oxyacetylated derivatives of ethylene glycol, glycerol, erythritol, a n d sorbitol, as well as the afore-mentioned inositol. T h e results, concludes Kullnig, clearly indicate the technique c a n b e used t o distinguish ketoses from aldoses, p e n t o pyranoses from pentofuranoses, cyciitois from polyols, a n d straight chain comp o u n d s from branched isomers.
rivatives—or rines. Because of their ability to rnirnic t h e p u r i n e molecules essential t o nucleic a c i d synthesis, these derivatives a p p e a r t o b e able to interrupt t h e normal c o u r s e of metabolism—be i t bacteria, f u n g u s , or human. This ability of t h e p u r i n e derivatives h a s stimulated intere s t i n preparing n e w compounds, a n d b e f o r e the Division of Medicinal C h e m i s t r y , a number of researchers revealed t h e i r progress in p r e p a r i n g such compounds. A general synthetic route t o purines bias b e e n worked out b y Joseph W . Xlarsico and associates of American Cyanamid. With the method the p u r i n e s can b e tagged easily by using e s t e r s of carbon-labeled orthoformate, t h u s facilitating studies of t h e metab o l i c pathways of t h e material. Among the compounds Marsico h a s synthesized are chloropurines; until n o w they have been obtained only b y chlorination of purinones (hydroxyp u r i n e s ) , a p r o c e d u r e often unsatisfact o r y . With t h e n e w method, 4,5-diaminopyrimidines are refluxed with m i x t u r e s of alkyl orthoformates a n d carboxylic acid anhydrides to form m i x t u r e s of purines and N-acylpurines. T h e acylpurine is hydrolyzed by dilute a q u e o u s base to the corresponding p u r i n e . In t h e same way, 4,5-diaminopyrimidines b e a r i n g at t h e 2 and 6 p o sitions amino, chloro, dimethylamino, tiydrogen, hydroxyl, methyl, and methylthio substituents give t h e corres p o n d i n g purines i n good yield. T h i s new p u r i n e synthesis is being u s e d at Cyanamid to synthesize t h e arninonucleoside related to t h e antibio t i c puromycin. F r o m 6-cMoropurine p r e p a r e d b y the n e w method, t h e arninonucleoside from puromycin a n d a n a l o g s such a s 9-(3-amino-3-deoxy-£i>ribofuranosyl) - 6 - diethylarninopurine fciave been p r e p a r e d by L e o n Goldman a n d associates. Such aminonucleosides i n general h a v e u ypcuiuuidax activity i n m i c e . The arninonucleoside from purom y c i n has tumor-inhibiting activity.
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RESEARCH • Blocking 9. Roland K. Robins and Hs£ Hu Lin have chosen a different point of attack on the purine structure. The antitumor activity of 6-mercaptopurine and 6-chioropuxine is generally believed to involve incorporation of these molecules into nucleic acid tlirough ribosidation, so the N e w Mexico Highlands University chemists prepared compounds such as 9-methyl-6chloropurine and 9-methyi-6-mercaptopurine in which the 9 position is blocked by a methyl group. Thus ribosidation should be prevented. The syntheses involve standard preparation and cyclization procedures—similar to those Marisco and Goldman are using— beginning with the appropriate pyrimidine intermediates. Using this method, Robins has synthesized about 40 compounds. A number are being screened at Southern Research Institute; in preliminary studies 9-methyl-6-chloropurine shows promising antitumor activity against adenocarcinoma 755 in mice.
N e w Job for Inorganics Study of inorganic compounds reveals marked ion exchange properties in many oxides People b e g a n using inorgaruc ion exchangers, chiefly silicates, more than 50 J*«ES Inorganic Cnemistrvfllf years ago to p u rify water, b u t those used have never caught on elsewhere because of their limited stability i n other than neutral solutions. And e x cepting certain chromatographic -uses, mosdy nonaqueous, other inorganics have enjoyed litde attention as ion e x changers. However, a comprehensive study of inorganic compounds, made by Kurt A . Kraus and coworkers of Oak Ridge National Laboratory, shows a number of oxides and mixed oxides to h a v e
marked ion exchange properties. Their exchange rates, selectivitdes, and capacities are in general good enough t o indicate their use in typical ion exchange applications. The Oak Ridge group worked with several hundred different preparations of oxides and mixed oxides of a dozen different metals. Almost all of the insoluble oxides show both anion and cation exchange properties, depending on the medium, Kraus told the Division of Physical and Inorganic Chemistry during the symposium on heteropoly anions. Hydrous oxides of zirconium, tin, titanium, and others are, in general, anion exchangers i n acid solution and cation exchangers in basic solution;
Clue to Reserpine Activity
Reserpine... New compound with significant reserpine like activity
v Making New Tranquilizers Some tranquilizing activity resides in a relatively small portion of the reserpine molecule, thus providing an approach to tailor-making compounds w i t h reserpinelike activity but devoid of side effects—this is the conclusion of research at University of Maryland school of pharmacy. F. M. Miller and Myron S. Weinberg started from the observation that the trimethoxybenzoate ester portion of reserpine is essential for pharmacological effect; but of the several alkaloids possessing this basic ring structure, essentially only reserpine has this type of activity. Apparently this structure is not enough. Proceeding from knowledge of other pharmacologically active nitrogen-containing compounds, they synthesized trimethoxybenzoate ester compounds that also contain a nitrogen atom separated from another electronegative atom by two or three carbon atoms. Compounds ranging from t h e simple aminoethyl ester to the cyclohexane derivative have been prepared. So far only tertiary aminopropyl ester of trimethoxybenzoic acid has significant activity (one third that of reserpine). The corresponding primary aminopropyl ester is inactive, as is the tertiary aminoetliyl ester. Thus, Miller and Weinberg told the Medicinal Division, the oxygen and nitrogen must be separated by three carbons and the nitrogen atom must be tertiary. Next step in t h e research: incorporate both features in cyclohexane derivatives 4760
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