Structural and Stereochemical Studies

An A-ray study of the perchlorate salt showed that protonation of iodolupinine (5 R = I) did not result in conformational inversion.10 

One of the new alkaloids of Baptisia australis has a mass spectrum differing from that of tinctorine (6) only in the intensity of fragmentation peaks it is believed to be a stereoisomer of tinctorine and has been named isotinctorine. Another alkaloid, C17H22N203, from the same source is apparently a 13-acetoxy-anagyrine, since alkaline hydrolysis gives a compound with a mass spectrum identical with that of 13-hydroxyanagyrine (baptifoline) (7).2 The structures of the new Baptisia alkaloids clearly need further study. 

An X-ray analysis of salts of lupanine, (8) HC1 2H20 and (8) HC104 H20, showed that ring c was in a boat conformation (cf. Vol. 10, p. 68) infrared studies of the salts and of the anhydrous hydrochloride indicate that this conformation is retained in solution, but that ring c is changed to a chair confirmation in anhydrous lupanine perchlorate. Conformations of mono- and di-protonated salts of 17/5-methyl-lupanine, cr-isolupanine, and 17/ -methyl-cr-isolupanine were also discussed on the basis of i.r. data.11 

15-Oxosparteine perchlorate hemihydrate, cf. (9), has been shown by X-ray crystallography to have rings a, b, c, and d in chair, chair, boat, and half-chair conformations, respectively 12 the corresponding rings of 17-oxosparteine, cf. (9), are in chair, chair, sofa, and chair conformations.13 

Katrusiak, Z. Kaluski, and A. Perkowska, Acta Crystallogr., Sect. B. 1981, 37, 281. 

4- Hydroxylupanine 13-Hydroxylupanine esters a-Isolupanine N-Methylangustifoline 17-Oxolupanine 

dlvaricata,was assigned structure (4) the presence of the butenyl group is apparent from the mass spectrum, in which the base peak at m/ 207 arises by allylic cleavage, and from the n.m.r. 

A new alkaloid of Sarothamnus scoparius seems to be the same dehydrosparteine obtained in transformation of lupin alkaloids by plant cell cultures and regarded as 11,12-dehydrosparteine (10) 

13- dihydroxylupanine (11) on the basis of the m.ass spectrum, which is characteristic of a 13-hydroxylupanine but differs from that of 

13- and r2,13-dihydroxylupanine. The structure and absolute configuration of tsukushinamine-A (12) was reported recently (cf. Vol. 10, p.69 Vol. 12, p.76) and now two isomers, tsukushinamine-B (13) and -C (14) have been isolated from Sophora franchetiana tsukushinamine-A is converted into the C isomer by heating at 2O0°C. 

---

Benzene-induced solvent shifts have been used in structural and stereochemical studies in a number of sulphur-136-139 j phosphorus-containing compounds, ethylenedi-imine complexes and nitro-... 

Structural and stereochemical studies of saraines macrocyclic alkaloids of the sponge Reniera sarai. Guo, Y. Madaio, A. Trivellone, E. Scognamiglio, G. and Cimino, G. Tetrahedron, 1996, 52, 8341. 

Total chemical synthesis of a carotenoid is also an important step in structural and stereochemical studies (Section III,D). The total synthesis of vitamin A was first reported by Isler et al. (1947), and in 1950 the synthesis of )8-carotene was described by three groups (Karrer and Eugster, 1950 Inhof-fen et al., 1950a,b,c Milas et al., 1950). Since then, a large number of natural carotenoids and related compounds have been synthesized. Some of the historical aspects of this work were discussed recently by Weedon (1979) and Isler (1979). Chemical synthesis of carotenoids was also the subject of an extensive review by Mayer and Isler (1971). More recently, several additional aspects of the chemical synthesis of carotenoids have been discussed by Bestmann (1979) and Mayer (1979). 

Abe, A, Radin, NS, Shayman, JA, Wotring, LL, Zipkin, RE, Sivakumar, R, Ruggieri, JM, Carson, KG and Ganem, B (1995) Structural and stereochemical studies of potent inhibitors of glucosylceramide synthase and tumor cell growth. J Lipid Res, 36,611-621. 

Vicinal /hh couplings have been extensively applied by many authors in structural and stereochemical studies of natural products. Thus, they have been used by Guo and co-workers to establish the structure of four new ot-methylene-y-lactone-bearing cembrane diterpenoids from Lobophytum crassum. Further examples include two new sesquiterpenes isolated from Cyperus rotundus L. by Xu et three new eudesmanohdes, ten sesquiterpenes extracted from Inula helenium, by Ma et two lactone... 

Bali, D.K.L., Liokas, V., Garson, M.J., and Faulkner, D.J. (1990) Structural and stereochemical studies on brominated meroterpenoids from the Diclyoceratid sponge Cacospongia sp. Aust. 

Capon, R.J., Groves, D.R., Urban, S., and Watson, R.G. (1993) Spongiaquinone revisited structural and stereochemical studies on marine sesquiterpene quinones from a Southern Australian marine sponge, Spongia sp. Aust.J. Chem., 46,1245-1253. 

Zhang, W., Krohn, X, Ding, J., Miao, Z.-H., Zhou, X-H., Chen, S.-H., Pesticelli, G., Salvadori, P Kiutan, T., and Guo, Y.-W (2008) Structural and stereochemical studies of a a-methylene-y-lactone-bearing cembrane diterpenoids from a South China sea soft coral Lobophytum crassum. J. Nat. Prod., 71,961-966. 

---