The synthesis and antiallergic activity of a series of 2-hydroxy-N-1H-tetrazol-5-ylbenzamides and isomeric N-(2-hydroxyphenyl)-1H-tetrazole-5-carboxamides is described. A relationship between structure and intravenous antiallergic activity in the rat passive cutaneous anaphylaxis (PCA) test has been established using a Hansch/Free-Wilson model and used to direct studies toward potent derivatives. The contribution of physicochemical properties to activity is discussed. One member of this series, N-(3-acetyl-5-fluoro-2-hydroxyphenyl)-1H-tetrazole-5-carboxamide (3f), which was selected for further evaluation, has an ID50 value of 0.16 mg/kg po and is 130 times more potent than disodium cromoglycate (DSCG) on intravenous administration.

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The synthesis and antiallergic activity in the rat passive cutaneous anaphylactic reaction of a series of 2-phenyl-8-azapurin-6-ones are described. Early in the investigation, a linear free-energy equation was established in which the activity was related to the size and hydrogen bonding capacity of the ortho substituent in the phenyl ring. This relationship was used to provide guidance and limits for subsequent work leading to 2-o-propoxyphenyl-8-azapurin-6-one which is 40 times more potent than disodium cromoglycate. It is suggested that good antiallergic activity in this series is associated with coplanarity of the phenyl group with the azapurin-6-one which would be favored by a high degree of hydrogen bonding.

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Pyrido [l,2-6] [2,4] benzodiazepin-6(1 IH)-one and its 1,2.3,4,4a,5-hexahydro-derivative have been prepared.Some chemical properties and reactions of these novel ring systems have been explored. DURING attempts to synthesise compounds of potential biological interest, the betaine (2) was treated with phosphoryl chloride to give a product assigned the pyrido--1,2-b] [2,4]benzodiazepinone structure (4) on the basis of analytical and spectral evidence (see Experimental section). This synthesis was further explored.I t was found more convenient to prepare compound (4) and its S-chloro-and 10-methoxycarbonyl derivatives directly from the corresponding pyridinium salts [e.g. (l)] by treatment with sodium methoxide in methanol. Prer i a Br'_ ' c 2 ' a sumably the reagent abstracts hydrogen bromide leaving an iminopyridone which cyclises by nucleophilic attack \ COzMe NH2 (3) 1 0 15)on the ester function. However, treatment of compound (1) with benzylamine gave 2-(2-pyridy1)isoindolin-l-one (5); this reaction may be rationalised in terms of an initial Dimroth rearrangement to form the benzylaminopyridine (3) which cyclises to structure (5) under the basic conditions.Catalytic hydrogenation of the pyridobenzodiazepinone (4) afforded the hexahydro-analogue (6), which under more vigorous conditions suffered ring cleavage to give the amide (7). N-Alkylation of the hexahydropyridodiazepinones proved difficult, but the methyl (9) and ethyl (10) analogues were prepared from compound (6) by use of the appropriate alkyl tosylate and sodium hydride. Lithium aluminium hydride reduction of compound (6) and its alkyl derivatives removed the carbonyl function to give the octahydropyridobenzodiazepines ( l l ) , (12), and (13), respectively, but under more vigorous conditions compound (6) gave the benzylamine (8). Nitration of compound (6) afforded the %nitro-derivative but attempted halogenation was unsuccessful. v The formation, i n situ, of an imino-chloride from compound (6) and phosphoryl chloride, and subsequent treatment with ammonia, led to decomposition. Similarly, no tractable product was obtained by treatment of the imino-ether of compound (6) with ammonia.However a 6-amino-derivative (14) was prepared from the reaction of 2-amino-l-(2-cyanobenzy1)pyridinium chloride with sodium 2-ethoxyethoxide in 2-ethoxy-HC[ qoa O R (9) R = M e (10) R = Et 1 ethanol followed by treatment with hydrogen chloride: Treatment of compound (6) with methyl iodide gave a quaternary derivative (15), which on reduction with lithium aluminium hydride suffered cleavage of the 4a,12-bond to form the diazacycloundecene (IS), possibly via an internal Hofmann elimination. fJ-0 R (11) R = H . (12) R = M e (13) R = Et -N N H3+ (14) EXPERIMENTAL KFJ*-K$J 2-Anzino-l-(2-metlzoxycavbonyZbenzyl)~y~idiniunz Bromide \ (1) .-Bromine (49 nil) in carbon tetrachloride (300 ml) was