Ester chromophore

Sensitization is not possible since there is no low-lying excited state of the ester chromophore. 

Macralstonine, C44H54N4O5, crystallizes as colorless, rectangular rods, mp 293° (dec.), [a]D +27.5°, and contains one methoxyl, at least two C-methyl, and three, or possibly four, methylimino groups (33, 36). Its IR-spectrum discloses the presence of an imino or hydroxyl group, an alkoxyacrylic ester chromophore (peaks at 1652 and 1628 cm-1), and an o-disubstituted benzene nucleus. The formation of a derivative with dinitrophenylhydrazine indicates the presence of a potential carbonyl function. Macralstonine has also been reported to possess a marked hypotensive activity (36). 

There are three known types of alkaloid which contain the a-methyleneindoline carboxylic ester chromophore, those which are typified by tabersonine (XCII), akuammicine (CCXXV), and condylocarpine (CCXV), respectively. The first is excluded since it has a C20 skeleton as against the C19 skeleton of mossambine. The molecular formula of... 

These polymers were chosen for several reasons. The phosphorescence of the acetonaphthyl ester chromophore is intense at 77K, so that spectra of high quality are obtained. At the same time the quantun yield of intersystem crossing from Sj to Tj is 1.0, so that interference from singlet energy migration is not a problem. 

Since the j -alkoxy-acrylic ester chromophore is present in the part structure below (n.m.r. evidence, see later), it follows that the fragment ion mje 438 contains the lower reduced anhydronium base part with the j8-alkoxy-acrylic ester grouping and the C4H7O2 residue from the saturated e ring of the upper half. 

The following discussion is restricted to aromatic chromophores. Although the same applies to additional chromophores, e.g. the amino-acrylic-ester chromo-phore (roxburghines, Section 5), the alkoxy-acrylic-ester chromophore (serpen-tinine, Section 15), and the alkoxy-acrolein chromophore (macralstonine. Section 12, p. 269), these are as a rule readily recognised from characteristic i.r. and n.m.r. absorptions. 

Paucivenine (268), an amorphous alkaloid of M. balansae var. paucivenosus, contains indole, indoline, and saturated ester chromophores, and in its mass spectrum exhibits peaks characteristic of eburnane and tabersonine (both of which could be generated by transfer of H-2 to C-16 with fission of the 16-16 bond) together with peaks reminiscent of tabersonine. On the basis of these data. 

The nett Cotton effects for the 230-250 nm transition in the c.d. spectra of polyol per(4-chlorobenzoates) with various configurations and conformations have been calculated by summing the component exciton Cotton effects for all participating pairs of p-chlorobenzoate ester chromophores, the components having been determined in earlier work by Nakanishi et al. Reasonably good agreement was attained between the preferred conformations as determined from n.m.r. studies of the polyols and those indicated by the c.d. data recorded for their per(4-chlorobenzoate) derivatives. ... 

Of the two widely encountered types of enol-ester chromophore (XXVII-A and B) the NMR-spectrum establishes the presence in picra-... 

---