A-Hydroxyacylals

Im Verlauf dieser Untersuchungen wurde gefunden, daS sich N-(a-Hydroxyacyl)-lactame- und Diketopiperazine spontan zu Cyclolen cycli-sieren und z.T. recht stabil sein konnen. Als Ausgangsmaterial fiir die Synthese des Peptidteils (Schema (9)) des Ergotamins diente (3S 9S-... 

Ott, H., A. J. Frey, and A. Hofmann The Stereospccific Cyclolization of N-a-Hydroxyacyl-phenylalanydpirolin-lactam. Tetrahedron [London] 19, 1675 (1963). 

Figure 31 Bacillaene biosynthesis, (a) Structure of dihydrobacillaene and bacillaene. PksJ oxidizes the C14 -C15 bond after dihydrobacillaene has been synthesized. Also, note the a-hydroxyacyl N-cap. This particular N-capping has been reported very rarely. (b)a- and /3-Ketoreduction of a-KICto a-HIC. The KR domain of the first PKS module in PksJ is capable of reducing both the a-KIC amide and the /3-ketone in an NAD(P)H-dependent fashion. The order in which these two reductions occur is unknown. Ultimately, keto-reduction is followed by dehydration and enoyl reduction, (c) Theoretical structure of PPant ejection ions used to analyze PksJ ketoreduction. Right PPant ejection ion resulting from IRMPD of Acac-S-PksJ(T3-T4) incubated with PksJ. Mass shift of +2.017 Da corresponds with reduction of the /3-ketone. Left PPant ejection ion resulting from IRMPD of a-KIC-GABA-S-PksJ(T3-T4) incubated with PksJ. Shift of +2.015 Da is observed in PPant ejection ions.

A(-(Hydroxyacyl)hydroxylamines (e.g. 299) readily yield the corresponding A(-hydroxyperhydro-... 

Acetyl-2-raethyl-5,6-dihydro-4//-l,3,4-oxadiazine (295) is obtained in low yield (20%) by heating ()3-hydroxyethyl)hydrazine with an excess of acetic anhydride <84JOU65l>. 4//-l,3,4-Oxadiazin-5(6if)-ones (296) are prepared in variable yields (31-80%) by condensing A -(a-hydroxyacyl)aryl hydrazines (ArNHNHC0CR 20H) with a-haloacyl halides (R R CXCOCl) in hot benzene... 

The unique structure of the ergot peptides prompted several laboratories to investigate closer the chemistry of cyclols. The Swiss chemists by following the course of oxacyclol formation with simple model components obtained cystalline products from a-hydroxyacyl lactames as indicated in Fig. 3 in a supposed equilibrium reaction the cyclols here seem to be energetically favored. 

Ott, H., Frey, A.J. and Hofmann, A. (1963) The stereospecific cyclolization of N-(a-hydroxyacyl)-phenylalanyl-proline lactams. Tetrahedron, 19,1675-1684. 

Hydroxy fatty acid (HFA) A fatty acid with a OH group linked to carbon C2 (also referred to as a). Ceramide with a hydroxyacyl chain is referred to as ceramide-HFA. If the acyl chain is nonhydroxylated, the ceramide is referred to as ceramide-NFA. 

The biosynthetic production of PHAs is the most important and investigated, and is the only method that has been developed to commercialization. There are three possible metabolic pathways involved in the biosynthetic production of PHAs, which have been reviewed elsewhere.In simplified form, the carbon source is converted to a hydroxyacyl-CoA thioester, the monomer which is polymerized to PHA, involving different metabolic pathways depending on the carbon source (Figure 6.2). 

Phenylsulfonyl)-3-phenyloxaziridine (1S6. Davis reagent. Figure 11.61) has been shown to react with sodium enolates of chiral carboximides of the Evans-Oppolzer type, providing a-hydroxyacyl derivatives with diastereoselectivities of 90-98% d. g 92,133 Subsequent titanium(IV) isopropoxide-mediated transesterification with benzyl alcohol and hydrogenolytic debenzylation releases the free a-hydroxy acids in enantiomerically pure form and in yields of 65-75%. This procedure was applied... 

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