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Thc intramolecular reaction of Na-formyltryptophan to 3,4-dihydro-13-carboline-3-carboxylic acid is realized with high yield either in trifluoroacetic acid or in formic acid -concentrated hydrochloric acid solutions. Optically active products are obtained when fornlylated L-or D-tryptophan are used as starting compounds. The cxpcrimental conditions employed are highly specific and the cyclization of N"-formyltryptophyl rcsiduc is rcal~zcd also in pcptides without secondary lytic reactions. The general behavior of Nu-forn~yltryptophan in formic acid solutions is discussed.Canadian Journal of Chemistry, 46, 3404 (1968) Scheme 1 The compounds containing the P-carboline nucleus are of great interest in connection with their occurrence in some alkaloids. A synthetic procedure available to obtain the members of this class consists in a condensation of tryptophan, or its simple substituted derivatives, with aldehydes to yield a 1,2,3,4-tetrahydro-P-carboline (1). These products can be converted t o the fully aromatic conlpounds by dehydrogenation. Some difficulties arise when the 3,4-dihydro-Pcarboline nucleus is desired. The partial dehydrogenation is generally difficult to realize since the dihydro derivatives are completely aromatized a t a rate that does not permit their accumulation ill the reaction medium. An alte~mative procedure to synthesize the 3,4-dihydro-P-carboline nucleus has been pointed out by Spath and Lederer (2) who directly converted the amides of tryptanline to the corresponding 3,4-dihydro-Pcarboline.The attempts to effect an analogous cyclization on Nu-acyltryptophan to obtain 3,4-dihydro-Pcarboline-3-carboxylic acids showed that secondary reactions such as decarboxylation and dehydrogenation occurred and in the case of Na-formyltryptophan no product was obtained (3,4). 'Contribution No. 15 The present report is concerned with the preparation of optically active 3,4-dihydro-P-carboline-3-carboxylic acid by cyclization of Nuformyltryptophan. The reaction conditions are also used to cyclize some Nu-formyltryptophyl peptides to obtain the corresponding 3,4-diliydro-P-carboline derivatives in good yields as depicted in Scheme I.Experimental Ultraviolet (u.v.) spectra were recorded with a Cary model 15 (I cnl cells) spcctrophotonieter. Anlino acid analyses were performed with a Becknian an~ino acid analyzer model 120 B using ~i~icrocells with a 6.6 rnm light path. Paper chromatography was carried out on Whatman No. 1 paper. The two solvents eniployed were aqueous solutions of ammonia 5 % (v/v) and a~nnionium chloride 3 % (w/v). 3,4-Diliydro-!3-carboline derivatives were easily detected as yellow fluorescent spots in U.V. light (4). Na-forniyltryptoplian was obtained by treatnient of the amino acid with o n e equivalent of acetic anhydride in formic acid (5). Na-for~nyl-L-tryptophyl-L-phenylalan.ine methyl ester, No-formyl-L-tryptophyl-L-tyrosine iiiethyl ester, and No-fonnyl-L-tryptophyl-L-leucine nlethyl ester were syntliesized froni Na-forniyl-L-tryptophan, and the corresponding amino acid est...

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