Carboline, 1-acetyl

Acetyl-3-methoxycarbonyl-/ -carboline, the alkaloid of Vestia lycioides, has been synthesized by two routes 200,6 the second involves the benzylic oxidation-dehydrogenation of l-ethyl-3-methoxycarbonyl-l,2,3,4-tetrahydro-/ -carboline by means of selenium dioxide in dioxan. A by-product in this oxidation was 1 -acetyl-/ -carboline, which occurs in Ailanthus malabarica. An extension of this reaction led to a simple two-stage synthesis of canthin-6-one (22) from Ab-benzyltryptamine and a-ketoglutaric acid (Scheme 2).206... 

Acetylation of a 3,4-dihydro-j8-carboline derivative has been reported. O. Fischer described an A-acetylharmaline which was formulated as 310 since on controlled permanganate oxidation it yielded a neutral product (311), which on hydrolysis gave 7-methoxy-l-oxo-l,2,3,4-tetrahydro-j8-carboline (313) the constitution of 313... 

Acylation of l,2,3,4-tetrahydro-j8-carboline derivatives takes place preferentially at the pyr-N. Thus l,2,3,4-tetrahydro-j8-carboline yields a 2-formyl and a 2-acetyl derivative, which give 2-methyl- ... 

Heat 85.5 g 3-carbethoxy-2-piperidone and 30 g KOH in 1 L water for twelve hours at 30°. Filter, cool to 0°, add 50 ml 6N HCI. Prepare a fresh solution by diazotizing at 0-5° a mixture of 85 g 3-amino-4-Cl-acetophenone, 250 ml concentrated HCI and 750 ml water with a solution of 36 g Na nitrite in 125 ml water. Add the piperidone solution at 0° to the diazonium salt solution and stir five hours at 10°. Filter, wash precipitate with water to get 80% yield of the hydrazone (1) (recrystallize-95% ethanol). Reflux 62 g (I) in 310 ml 88% formic acid to get 40 g of the carboline (II) (recrystallize-absolute ethanol) (test for activity). Reflux 40 g (II), 100 g KOH, 480 ml ethanol and 360 ml water for eighteen hours and evaporate in vacuum. Add 480 ml water to the residue, cool and adjust pH to 6 with glacial acetic acid. Scratch glass to precipitate filter, wash precipitate with cold water to get 41 g 4-acetyl-2-COOH-7-CI-tryptamine (recrystallize-50% ethanol) which can be alkylated to the active dialkyltryptamine as described elsewhere here. 

Banisteriopsis caapi The primary hallucinogenic constituents of B. caapi are the jS-carbolines. These include harmaline, tetrahydroharmine, harmol, harmic acid methyl ester, harmic amide, acetyl norharmine, harmine A/-oxide, harmalinic acid, and ketotetrahydronorharmine (figure 9.8). B. rusbyana also contains DMT, as well as A/-methyltryptamine, 5-methoxy-N,/V-dimethyltryptamine, and 5-hydroxy-N,/V-dimethyltryptamine (bufotenin). /V-methyltetrahydro-jS-carboline is found in trace amounts. 

For the preparation of 3,4-dihydro-/3-carbolines the Bischler-Napieralski reaction is widely used (510R74). Since this reaction requires rather drastic conditions, A-acetyl tryptophan and its analogs yielded l-methyl-/8-carboline (harman) rather than l-methyl-3,3-dihydro-j8-carboline-3-carboxylic acid derivatives owing to accompanying decarboxylation and aromatization (41JCS153 50JA2962). 

For the synthesis of the natural blue pigment trichotomine dimethyl ester, L-Trp-OMe was used as a starting material. The first step of this synthesis was conversion into methyl l-methyl-3,4-dihydro-/8-carboline-3-carboxylate with acetyl chloride in TFA (85JOC3322). An improved method starts from the corresponding thioamides via thioiminium salts which cyclize spontaneously in refluxing solvent (82CPB4226). A-Formyl-tryptophan also cyclized readily with no side reactions (68CJC3404). 

The acyl-Pictet-Spengler reaction is also catalyzed by chiral thiourea derivative 6 to provide M-acetyl p-carbolines in high enantioselectivities. Notably, thiourea derivatives can activate not only electronically distinct imine derivatives such as N-alkyl and N-Boc imines but also a weakly Lewis basic N-acyhminium ion with high enantioselectivity using a chiral hydrogen bond donor (Scheme 12.4). 

The synthesis of /./-pyridindolol 1064 started by acetonation of glyceric ester 1057 to give 1058, which was converted to the imidazoline 1059 by reaction with l,l-dimethyl-l,2-diaminoethane followed by acetylation. Its methylation gave 1060, which can be reduced to 1061 further reaction with tryptamine or tryptophan ester hydrochloride 1062 gave the respective diastreomeric mixture of carboline 1063 (80H947). Its conversion to racemic alkaloid d,/-pyridindolol 1064 could be readily achieved (79JOC535). 

In 2004, Taylor and Jacobsen suggested a procedure for the enantioselective acetyl-Pictet-Spengler reaction, that is the cyclization of electron-rich aryl or heteroaryl groups onto N-acyliminium ion enabling access to substituted tetrahydro-P-carbolines and tetrahydroisoquinolines that are core structure elements in natural and synthetic organic compounds [202, 203]. Screening various thiourea catalyst candidates such as 47 in the formation of model product Np-acetyl-... 

Scheme 6.50 Typical tetrahydro-P-carbolines prepared with the 52-catalyzed enantioselective acetyl-Pictet-Spengler reaction.

The root bark of Ailanthus altissima Swingle contains the known alkaloids canthin-6-one (22), l-methoxycanthin-6-one, canthin-6-one A-oxide, and 1-acetyl-4-methoxy-/ -carboline, together with three new alkaloids, identified as 1-methoxy-canthin-6-one A-oxide, l-(2-hydroxyethyl)-4-methoxy-/ -carboline, and 1(1,2-dihydroxyethyl)-4-methoxy-/ -carboline.21... 

The structure inhibitory activity relationships among numerous P-carboline alkaloids was studied. Harmine was found to inhibit the actions of cyclic adenosine monophosphate (cAMP) phosphodiesterase (ICS0 69.3 x 10 5 M). Among the di- and tri-substituted P-carbolines, the O-methylated P-carbolines and the O-acetylated p-carbolines had higher inhibitory activity than the corresponding hydroxy p-carbolines, while the dihydro- and tetrahydro-derivatives were not potent inhibitors [271]. 

Acylation of 3-substituted indoles is more difficult, however 2-acetylation can be effected with the aid of boron trifluoride catalysis." " Indoles, with a carboxyl-containing side-chain acid at C-3, undergo intramolecular acylation forming cyclic 2-acylindoles." Intramolecular Vilsmeier processes, using tryptamine amides, have been used extensively for the synthesis of 3,4-dihydro-p-carbolines, a sub-structure found in many indole alkaloids (P-carboline is the widely used, trivial name for pyrido[3,4-fc]indole). Note that it is the imine, rather than a ketone, that is the final product the cyclic nature of the imine favours its retention rather than hydrolysis to amine plus ketone as in the standard Vilsmeier sequence " this ring closure is analogous to the Bischler-Napieralski synthesis of 3,4-dihydro-isoquinolines (9.15.1.7). 

Villagorgin A (55) inhibits acetylcholine induced contraction of guinea-pig ileum and thrombin and calcium ionophore A23187 induced aggregation of human platelets, a calcium-calmodulin mediated event (54). Several of the simple P-carbolines are cytotoxic (Table 1). 1-Acetyl-p-carboline (63) is cytotoxic toward brine shrimp causing 100% mortality in 24 hr (61). 

Scheme 17. Hannan [1], 1-ethyl-p-carboline [2], S-l-(l -hydroxyethyl)-P-carboline [3], and pavet-tine [4] from the bryozoan Costaticella hastata. 1-Acetyl-P-carboline [5] are known from Arenaria kansuensis.

The P-carboline alkaloids harman [1] and pavettine [4] from the bryozoan Costaticella hastata (207) are known from numerous terrestrial plants. Still another bryozoan compound (S)-1-(l -hydroxyethyl)- P-carboline [3] is new but closely related to 1-ethyl-P-carboline [2] present in the bryozoan. It is also known from the roots of Hannoa klaineana (Simaroubaceae) (208) and 1-acetyl-P-carboline [5] from Arenaria kansuensis (Caryophyllaceae) (209). Incidentally, pavettine [4] was detected in only one collection of the bryozoan. 

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