Enantioselective Preparation of b 2 -Amino Acid Derivatives for b-Peptide Synthesis b 2 -A m i n o A c i d D e r i v a t i v e s f o r b -P e p t i d e S y n t h e s i sAbstract: b-Amino acids with a single side chain in the a-position (b 2 -amino acids or H-b 2 hXaa(PG)-OH; i.e., homo-amino acids with proteinogenic side chains) have turned out to be important components in b-peptides. They contribute to unique secondary structures, they are required for mimicking the structure and the activity of bturn-forming a-peptides, and they can be used for protecting a-peptides against attack by aminopeptidases. In contrast to b 3 -homoamino acids, the b 2 -isomers cannot be obtained simply by enantiospecific homologation of the (natural) a-amino acids, but have to be prepared by enantioselective reactions or sequences of transformations, which are presented herein. The various preparative methods are ordered according to the bond at the stereogenic center, which is formed in the stereoselective step, with the four strategic bonds being the C(2)-C(3) backbone bond, the C(2)-side-chain bond, the C(2)-H bond, and the C(1)-C(2) bond between the carboxylate and the a-carbon. In the most frequently employed methods, a chiral auxiliary group is attached at the carboxyl C(1) atom or at the nitrogen in the 3-position, but there are also a number of enantioselective catalytic processes, including the hydrogenation of suitable acrylates. The alternative of stereoselective synthesis, namely resolution of racemic mixtures (for instance by biocatalysis), is also discussed. A critical comparison of the various methods and strategies is presented. For the peptide chemist, a list is included with the Cbz-, Boc-, and Fmoc-protected b 2 -amino acid building blocks, ready for peptide coupling. In addition, the search strategy for nonracemic b 2 -amino acids and their precursors from the databases is described in detail. 10Detailed Search Strategy 11Conclusions and a Table with b 2 -Amino Acid Building Blocks for Peptide Synthesis

Fall leaves of the common wych elm tree (Ulmus glabra) were studied with respect to chlorophyll catabolites. Over a dozen colorless, non‐fluorescent chlorophyll catabolites (NCCs) and several yellow chlorophyll catabolites (YCCs) were identified tentatively. Three NCC fractions were isolated and their structures were characterized by spectroscopic means. Two of these, Ug‐NCC‐27 and Ug‐NCC‐43, carried a glucopyranosyl appendage. Ug‐NCC‐53, the least polar of these NCCs, was identified as the formal product of an intramolecular esterification of the propionate and primary glucopyranosyl hydroxyl groups of Ug‐NCC‐43. Thus, the glucopyranose moiety and three of the pyrrole units of Ug‐NCC‐53 span a 20‐membered ring, installing a bicyclo[17.3.1]glycoside moiety. This structural motif is unprecedented in heterocyclic natural products, according to a thorough literature search. The remarkable, three‐dimensional bicyclo[17.3.1]glycoside architecture reduces the flexibility of the linear tetrapyrrole. This feature of Ug‐NCC‐53 is intriguing, considering the diverse biological effects of known bicyclo[n.3.1]glycosidic natural products.

Chemistry of α‐Aminonitriles I: Introduction and Pathways to Uroporphyrinogen‐octanitriles. An introduction to experimental studies on the chemistry of α‐aminonitriles potentially relevant to the problems of prebiotic chemistry is presented. The framework of conditions wherein the investigation is chosen to be carried out implies both molecular oxygen and ‐ whenever feasible ‐ water to be excluded from reaction conditions. This study focusses on 2‐amino‐2‐propenenitrile (3) (Scheme 6) as central starting material of reaction sequences which aim at the nitrile forms of proteinogenic amino acids as well as at the aza forms of building blocks of biological cofactor molecules as their targets (Scheme 5). Schemes 13,16,23 as well as 25 and 26 summarize reaction sequences by which 3 is transformed within the defined framework of conditions into the thermodynamic (statistically controlled) mixture of the four isomeric uroperphyrinogen‐octanitriles 57–60. HPLC's of such mixtures document the dominance of the least symmetrical isomer whose constitutional pattern of peripheral substituents happens to be the one percent in all biological porphinoids. Preparative procedures for the synthesis of 3(Scheme 9), the β,β‐disubstituted pyrrol‐nitriles 30,53 and 54 (Scheme 19) as well as the porphyrinogenoctakis(propionitrile) and‐octakis(acetonitrile) 65 and 66, respectively (Scheme 24) are given.

Edgardo Giovannini zum 70.Geburtstag gewidmet (3 1. I. 79) Bacteriochlorophyll acg and Bacteriopheophytin ap in Photosynthetic Reaction Centers fromRhadospiriuum rubrum G-W Summary In photosynthetically active reaction centers from Rhodospirillum rubrum G-9+, the magnesium complex bacteriochlorophyll a contains geranylgeraniol as the alcohol component, while the metal-free bacteriopheophytin a contains phytol instead. These pigments bacteriochlorophyll acg (4) and bacteriopheophytin ap (1) were isolated from reaction center preparations in a ratio of 2: 1 and (after demetallation of 4) identified as bacteriopheophytin acg (2) and ap (1) by comparison with authentic samples (UV./VIS., CD. and mass spectra as well as mixed HPLC.).Untersuchungen der Chlorophyll-Pigmente in Photosynthese-Reaktionszentren (= 'Set of molecules that can effect the photochemical transfer of one electron' [2]) aus Rhodopseudomonas spharoides und Rhodospirillum rubrum ergaben einen Gehalt von vier Bakteriochlorophyllen a und zwei Bakteriophiiophytinen a pro Fig. 9 im exper. Teil) war ca. 2,4 (Mittelwert aus sechs verschiedenen E~trakten'~)). Die beiden Pigmente wurden durch praparative DC. auf Kieselgel getrennt. Die Bakteriophaophytin-Fraktion (Ausbeute 54% 17)) zeigte im HPLC. ausser dem Hauptsignal (relative Pikflache 96,5) schwachere Pike vom 13*-Epimer 1' (0,9), Bakteriophaophytin aGg (2*O); 2,3) und einer Verunreinigung (0,3) (s. Fig. 10 Da das Ziel unserer Untersuchung die Charakterisierung der RC.-Haupipigmente Bakteriochlorophyll a bzw. Bakteriophiiophytin a und nicht eine vollstandige Analyse der porphinoiden RC.-Bestandteile war (vgl. auch Fussnote 181, sind unsere Kenntnisse iiber die Natur der beobachteten Nebenkomponenten unvollstandig. Charakteristisch fur diese Nebenprodukte war ihr schwankender Anteil in den Pigmentanalysen; ihr natiirliches Vorkommen als RC.-Bestandteile ist deshalb eher unwahrscheinlich. Die beiden zu 1 und 2 epimeren Bakteriophaophytine alp (1') bzw. a%, (2') fanden sich in meist kleinen, jedoch stark schwankenden Mengen (0,2-3.5% fur l', 0.5-8% fur 2'")); in drei Fallen ergaben sogar verschiedene HPLC.-Untersuchungen der gleichen Probe verschiedene Werte (s. [I], S. 188, 193 und 198). Diese beiden Epi-Bakteriophaophytine wurden vermutlich bei der Manipulation der Pigmente gebildet (zu deren sehr ieicht erfolgenden Epimerisierung vgl. oben). Analoges gilt fur verschiedene griine Oxydationsprodukte, die nicht bei allen Analysen auftraten (vgl. Fussnoten 54 und 56).Das i m DC. der RC.-Rohextrakte und der Bakteriochlorophyll-Fraktionen beobachtete polare blaue NebenproduktZ2) und die im HPLC. der ccphaophytinisiertenn Bakteriochlorophyll-Fraktionen gefundene polare Nebenkomponente sind sehr wahrscheinlich Oxydationsprodukte des Bakteriochlorophylls (moglichenveise an C ( 132) oxydierte sogenannte cc4Uomere)) [2 lc]), deren Menge von der Lagerungsdauer der RC.-Praparationen und der Arbeitstechnik abhiingig war. So fanden wir in einem orientierenden Vorversuch infolge offensichtlich ungeniigendem Sauer...

Introduction of Magnesium into Ligands of the Chlorophyll Series by (2,6‐Di‐t‐butyl‐4‐methylphenoxy)magnesium Iodide Experimental details are given for the new method of introducing magnesium into porphinoid ligands by (2,6‐di‐t‐butyl‐4‐methylphenoxy)magnesium iodide (1), previously published in preliminary form [1]. Besides magnesium octaethylporphyrinate (14), methyl pyrochlorophyllide a (10), methyl chlorophyllide a (8), and methyl bacteriochlorophyllide a (12), the complexation of pheophytin a (2) to chlorophyll a (3) and of pheophytin b (4) to chlorophyll b (5) are described.