Natural peptide libraries often contain cyclodepsipeptides containing α- or β-hydroxy residues. Extracts of fungal hyphae of Isaria yield a microheterogenous cyclodepsipeptide mixture in which two classes of molecules can be identified by mass spectral fragmentation of negative ions. In the case of isaridins, which contain an α-hydroxy residue and a β-amino acid residue, a characteristic product ion corresponding to a neutral loss of 72 Da is obtained. In addition, neutral loss of water followed by a 72 Da loss is also observed. Two distinct modes of fragmentation rationalize the observed product ion distribution. The neutral loss of 72 Da has also been obtained for a roseotoxin component, which is also an α-hydroxy residue containing cyclodepsipeptide. In the case of isariins, which contain a β-hydroxy acid residue, ring opening and subsequent loss of the terminal residue as an unsaturated ketene fragment, rationalizes the observed product ion formation. Fragmentation of negative ions provide characteristic neutral losses, which are diagnostic of the presence of α-hydroxy or β-hydroxy residues.

天然肽库通常包含含有 α- 或 β- 羟基残基的环缩肽。的真菌菌丝提取物棒束孢产生微异质环缩肽混合物，其中可以通过负离子的质谱碎片鉴定两类分子。对于含有一个 α-羟基残基和一个 β-氨基酸残基的鸢尾素，获得了对应于 72 Da 的中性损失的特征产物离子。此外，还观察到水的中性损失，然后是 72 Da 的损失。两种不同的碎裂模式使观察到的子离子分布合理化。玫瑰毒素成分也获得了 72 Da 的中性损失，该成分也是含有环缩肽的 α-羟基残基。对于含有 β-羟基酸残基、开环和随后作为不饱和烯酮片段的末端残基丢失的鸢尾素，使观察到的产物离子形成合理化。