Alkaloids of the Apocynaceae

Extraction of the leaves of Holarrhena curtisii that had grown in Thailand yielded the known constituent holacurtine (6a) together with a new alkaloid.6 The latter was assigned the structure A-desmethylholacurtine (6b) on the basis of spectroscopic comparison with holacurtine. The H n.m.r. spectrum of A -acetyl-holacurtine (6c) showed two resonances each for the 0-methyl, A-methyl, and secondary C-methyl groups, which was interpreted to mean that the amide group 

6-Dihydro-5,6-dihydroxyconessine has been prepared by the action of aqueous nitrous acid on conessine (7a).7 Treatment of conessine with BrCN yields the 7V-cyano-iV-desmethyl derivative (7b).8 The latter has been converted (by standard methods) into derivatives (7c), (7d), and (7e).9 

In a study of the Hofmann-Loffler reaction, the jV-chloro-amine (8a) was irradiated in trifluoroacetic acid solution and underwent photolysis to yield the pyrrolidine (9a) together with the 205-isomer (9b) in a ratio 8 1. The starting amine (8b) was prepared by hydrogenation of (8c), followed by von Braun demethylation and hydrolysis of the JV-cyano-amine (8d) which was so formed. The n.m.r. spectrum of (8b) and of related amines in the presence of lanthanide shift reagents was discussed.10 

Details are now available of the reactions of peracids and of hydrogen peroxide with the imines (10) and (11). The reactions of the product oxaziridines and nitrones with the same two oxidants were also discussed. The reactions of sodium borohydride, benzoyl chloride, and toluene-p-sulphonic acid with the hydroxy-nitrones (12) and (13) have been reported.12 The c.d. spectra of 2-substituted pyrrolidines have been compared with that of conanine (14).13 

Acid-catalysed hydrolysis of the carbamate (15a)14 gave the amino-pregnane (15b).15 The latter amine underwent a condensation reaction with 3,5-di-t-butyl-o-quinone to yield an anil which gave progesterone (15c) on hydrolysis with an acetate buffer.16 Other amino-pregnane derivatives have been prepared by degradation of solasodine17 (vide infra). 

Five new pyrrolizidine alkaloids, each containing a novel fourteen-membered macrocyclic ring, have been isolated by Edgar et al.x Parsonsine (44) and heterophylline (45) were present in Parsonsia heterophylla A. Cunn. and P. spiralis Wall., while spiraline (46), spiranine (47), and spiracine (48) were obtained only from P. spiralis. These five alkaloids are derived from retronecine that is esterified at C-9 with (-)-trachelanthic acid i.e. indicine), and further diesterified by a series of substituted malic acid derivatives to complete the fourteen-membered ring. Indeed, partial hydrolysis of parsonsine (44) yielded indicine (49). The non-equivalence of the C-9 protons (ABq, S 4.45 and 5.20 p.p.m.) in parsonsine indicates the presence of a macrocyclic system, and 

Culvenor, and A. T. Dick, The Pyrrolizidine Alkaloids , North-Holland, Amsterdam, 1968. 

Another new alkaloid (50) was also isolated from P. heterophylla. Mild acid hydrolysis of (50) gave a desacetyl compound which showed a prominent peak due to the loss of —CH2C02CH3 in its mass spectrum, thereby indicating that the other carboxyl group is esterified to the base. Vigorous acid hydrolysis of (50) gave 1-hydroxymethylpyrrolizidine of undefined stereochemistry together with a neutral compound which yielded (-)-2-isopropylmalic acid on basic hydrolysis. 

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Steroidal Alkaloids of the Apocynaceae and Buxaceae and Related Compounds , F. Khuong-Huu and R. Goutarel, in Alkaloids , ed. M. F. Grundon, Royal Society of Chemistry, London, 1977, vol. 7, pp. 268-288. 

A number of our regular authors are not participating this year, and I would like to express my appreciation to Drs. Crout and McCorkindale for their contribution to Volumes 6 and 7 and in particular to Drs. Goutarel and Khuong-Huu for reviewing steroidal alkaloids of the Apocynaceae and Buxaceae since the inauguration of this series of Reports in 1971. In this Volume, all steroidal alkaloids are included in Chapter 14. 

Steroidal Alkaloids of the Apocynaceae and Buxaceae and Related Compounds... 

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