Neo-series

The exceptional nthetic utility of a saturated analogue (218) has been demonstrated in the brilliant total nthesis of cephalosporin C and analogues by Woodward (151-160]. The important work of CIBA-Geigy A.G. and the Woodward Forschungsinstitut in this respect has been discussed in Part I, and readers are referred to one particular reference [161]. For the chemistry of these useful nthetic intermediates (217) and (218), see some recent reviews [162-168]. 

An interesting transformation of penicillin sulphoxides to 5,6-dithia-8-aza-7-neoctem derivatives (225) is to be mentioned here. 

Yields of the reaction (224)- (225) are almost quantitative, and further steps lead to 3-cephems in a high overall yield. 5-Thia-7-azaoct-6-em derivatives (228) also give 3-cephems upon treatment with HgO/I [176]. 

Penicillins (1) were the first group of natural products found to contain a 0-lactam ring. Other compounds from different sources in nature, however, have also turned out to contain a 0-lactam ring, either in monocyclic form, or as part of a bicyclic system, as in the cephalosporins (2). 

Cephalosporin C (236a) (see Table 4.7) was one of the constituents of a crude mixture of antibiotics obtained from a culture of Cephalosporium species by Brotzu [177]. The stematic work of Abraham in Oxford led to the isolation and structural studies of this compound [178]. Differences from the penam system were pointed out [179,180] and the proposed dihydrothiazine—aze-tidinone structure was confirmed by chemical [181] and X-ray methods [182]. Tliis compound has also been obtained from several other organisms [183—185]. 

---

Treatment of vitamin Bi2 with strong acids, such as trifluoroacetic acid, gives a second series of pigments which are slightly darker than the normal ones they are the so-called neo series and have been identified (71JCS(C)3736) as the 13-epimers, e.g. (251), of the natural compounds. 

One major difficulty connected with structure XX at this stage was the position and degree of substitution of the olefinic bond in the neo series. Much experimental work had been carried out, but the results were difficult to interpret. This question was finally solved independently... 

The other use to which electrolytic reduction was put was the reduction of the double bond in the neo series. The reducibility of the neo double bond under these conditions was, in fact, taken to be support for its enamine character. By this method, neostrychnidine was reduced at 100° to dihydrostrychnidine-A and methoxymethyldihydroneostrych-nidine (LXVII) at 15° to methoxymethyltetrahydrostrychnidine (LXVIII R = OCH3) (76). The conversion of CIX into CXI has also been carried out electrolytically (107). 

Analogous changes were observed in other neo-bases, in one of which the compound corresponding to CCXV was reduced back to the neo-series by zinc and hydrochloric acid. If this sequence should prove correct, it would provide an interesting addition to the known collection of acid-catalyzed rearrangements, but further experiment is clearly indicated before this scheme can be considered to be fully established. 

For bicyclic /3-lactams of other types he suggests the names neoheptam (9), neooctam (10), etc. In this neo -series the suggested numbering system is based... 

Usually not favorable for separation of components that show similar Hquid-phase behavior, ie, steroisomers, homologous series, iso-notmA—neo isomers components to be separated must have some different functional group for MSA to affect Hquid-phase behavior differently. 

Note The B and C series of the PSP (R4 - SO ) have not been included in this table because they form their STX, NEO and GTX counterparts (11) on treatment with acid during the preparation of clam extracts. For the structure of tetrodotoxin see (8,9). 

Marketing of 1 1-chromium complex dyes as Palatin Fast serie (BASF) and Neo-Ian serie (Ciba)... 

Although a structure was published for VI/1, it was not crystallized, despite many attempts at purification. By TLC, samples of oncinotine always seemed to contain some iso-oncinotine (VI/3). Subsequently, it was learned that the crude oncinotine contained another isomer, VI/2, neo-oncinotine, but no iso-oncinotine. During the purification attempts, it appeared that VI/2 was converted to VI/3 (Scheme VI/1) [2]. This reaction has been the starting point of a series of investigations in the field of transamidation reactions. 

Spectra near the Ar16+ Rydberg series limit [11] are shown in Fig. 7.8. The top spectrum was taken along the central chord of a plasma with neo = 0.9 x 1020/m3 and Teo = 2600 eV. The resonance lines from W6 to... 

Figure 5 Overview of glycolipid biosynthesis. Mammalian glycosphingolipids (GSLs) are synthesized from Cer after the addition of Gal, to form the small GalCer-series, or after the addition of Glc and Gal to form the ubiquitous LacCer class, which is subdivided into gangliosides, globosides, and the neo-lactoseries. Additional information on the enzymes and specific GSLs shown can be found in the KEGG databases (see the Legend for Fig. 3).

The kestose or fructan series of sucrose-related oligosaccharides is found in at least 12% of vascular plant species [23]. Kestoses contain one glucose moiety per oligosaccharide chain, derived from the parent sucrose molecule by the action of fmctosyltransferases. The simplest kestose, monofructosyl-sucrose is a trisaccharide that exists as three isomers 1-kestose (l - 8-D-fructofuranosylsucrose), 6-kestose (6 - -D-fructofuranosylsucrose), and neo-kestose (6 - -D-fructofuranosylsucrose). These isomers form the basis of three major kestose subseries with different linkage patterns [23]. 

---